Child development, ages 0 to 18: a free parent guide

Introduction

How to use this guide

Jump to your child's age in the table of contents, or read straight through. Each part covers what is typical, how children of that age learn, what helps at home, and when to ask for help. Part 6 covers topics that run across every age, such as sleep and screens. Part 7 and the appendices list resources, screening tools, a glossary and printable checklists.

Two words come up a lot: typical means what many children do around that age, and range means the spread of ages at which healthy children reach a skill. Neither is a test your child passes or fails.

Understanding developmental ranges, not deadlines

The milestones in this guide come mainly from the CDC's "Learn the Signs. Act Early." checklists, revised in 2022 with the American Academy of Pediatrics (AAP). The revised checklists list skills that most children (about 3 in 4) are expected to show by each age. That change was made on purpose: the old lists used the age when about half of children had a skill, which encouraged "wait and see" when a child was behind.^[1]

So, read the lists this way:

• A missed milestone is not a diagnosis. It is a good reason to bring it up with your child's doctor.
• Children often move ahead fast in one area (say, walking) while another area (say, talking) takes longer.
• Babies born early are usually measured from their due date, not their birth date, in the first two years. Ask your doctor how this applies to your child.
• Losing a skill a child used to have is different from being slow to gain one. Mention any lost skill to your doctor promptly, at any age.

When and how to talk to a pediatrician or specialist

CDC advises acting early. Talk with your child's doctor if your child is not meeting one or more milestones, has lost skills they once had, or if you have any other concern.^[2] You do not need to wait for the next checkup.

What helps the conversation:

• Write down what you see, with examples and dates ("At 20 months she says two words; she used to say five").
• Bring a checklist. The free CDC Milestone Tracker app lets you check off milestones and share a summary with the doctor.^[3]
• Ask directly: "Can we do a developmental screening?" The AAP recommends a general developmental screening with a validated tool at the 9-, 18- and 30-month visits, and autism screening at 18 and 24 months, plus any time a parent has a concern.^[4]
• If you are still worried, ask for a referral to a specialist, such as a developmental pediatrician, a speech-language pathologist or an occupational therapist.

You can also contact services yourself, without a doctor's referral. For children under 3, that is your state's early intervention program. For age 3 and up, it is your local public school district (see When to seek early intervention or school services).

Trusted resources overview

Part 1: Infancy (0–12 months)

How babies learn. In the first year, babies learn through their senses and movement: looking, listening, mouthing, grasping and moving. They also learn through people. Researchers at Harvard's Center on the Developing Child call this "serve and return": the baby coos, points or cries, and an adult responds with eye contact, words or a hug. These everyday back-and-forth moments help build the brain connections that later support language, social and thinking skills.^[5] You do not need special toys or programs. Talking, singing, naming things and answering your baby's sounds are the work.

1.1 Sleep and soothing

Safe sleep comes first. The AAP's "ABC" for every sleep, naps included:^[6]

• Alone: no pillows, blankets, bumpers or soft toys in the sleep space, and no bed-sharing. Room-sharing (baby's own crib in your room) is recommended, ideally for at least the first 6 months.
• Back: on the back for every sleep. Side sleeping is not safe either, because babies can roll.
• Crib: a firm, flat surface that meets safety standards (crib, bassinet or play yard) with only a fitted sheet. If your baby falls asleep in a car seat, swing or carrier, move them to a flat sleep surface when you can. Never sleep with a baby on a couch or armchair.

The AAP also notes that swaddling does not lower SIDS risk and should stop once a baby shows signs of rolling, and that home breathing monitors do not lower SIDS risk.^[6]

How much sleep? For babies 4 to 12 months, sleep experts recommend 12 to 16 hours per 24 hours, naps included. For babies under 4 months, sleep varies too much for a single recommendation.^[7]

Soothing. Crying is how babies communicate. Common soothing tries: feeding, a diaper change, holding and rocking, white noise, a pacifier at sleep time once feeding is established, and a calm, dim room. If you feel overwhelmed, it is always okay to put your baby down safely in the crib and step away for a few minutes. If crying seems unusual for your baby, or comes with fever, poor feeding or other worries, call your doctor.

1.2 Feeding, growth and physical care

• Growth is tracked at checkups. Your doctor plots weight, length and head size on a growth chart. The pattern over time matters more than one number.
• Feeding cues. Around 4 months, many babies open their mouth when they see the breast or bottle; by 6 months, many close their lips to show they are done.^[2]
• Starting solids. Ask your doctor when your baby is ready for solid foods, and how to introduce them.
• Regular well visits and vaccines are part of keeping babies healthy and are also listed by the AAP among ways to lower sleep-related risks.^[6]

1.3 Early motor and sensory milestones

What most babies do by each age, from the CDC checklists (a selection; the full lists are longer):^[2]

Tummy time while your baby is awake and watched helps build the neck, shoulder and arm strength used for rolling, sitting and crawling.^[6]

1.4 Resources for infants

• CDC milestone checklists, 2 to 12 months
• AAP: A parent's guide to safe sleep
• Harvard Center on the Developing Child: serve and return
• Free from UpOnly Learning: our free resources page is mostly for ages 4 and up today, but the habit that matters most at this age, talking and reading together every day, costs nothing.

Part 2: Toddlers (1–3 years)

How toddlers learn. Toddlers learn by doing: moving, copying adults, handling real objects and, by about 2½, pretending. Language usually grows fast in this period. Research suggests that the amount of back-and-forth conversation a child has with adults (not just how many words they hear) is linked to stronger language skills and language-related brain activity.^[8] Narrate your day, ask simple questions, wait for an answer and build on it.

2.1 Motor development

What most toddlers do, from the CDC checklists:^[2]

• 15 months: takes a few steps alone; feeds self with fingers.
• 18 months: walks without holding on; scribbles; drinks from a cup without a lid (may spill); climbs on and off a couch or chair.
• 2 years: kicks a ball; runs; walks (not climbs) up a few stairs with or without help; eats with a spoon.
• 30 months: uses hands to twist things like doorknobs or lids; takes some clothes off; jumps off the ground with both feet; turns book pages one at a time.

Safe chances to climb, run, throw and build every day are the best "practice."

2.2 Language and communication

• 15 months: tries to say one or two words besides "mama" or "dada"; points to ask for something.
• 18 months: tries to say three or more words besides "mama" or "dada"; follows one-step directions without gestures ("give it to me").
• 2 years: puts two words together ("more milk"); points to things in a book when you ask; points to at least two body parts.
• 30 months: says about 50 words; puts two or more words together with an action word ("doggie run"); uses words like "I," "me" or "we."^[2]

"Is it normal for a 2-year-old not to talk?" Toddlers vary a lot, and many late talkers catch up. Still, by the CDC's 2022 checklists most children are putting two words together by 2. If your child is not, or is not pointing, responding to their name, or understanding simple words, ask your doctor about a screening and a hearing check. Early help is free for eligible children under 3 (see early intervention).

2.3 Behavior and emotional regulation

Tantrums are a normal part of this age. Toddlers want independence but do not yet have the words or self-control to handle big feelings. What tends to help:

• Keep routines predictable, and give a heads-up before changes ("two more minutes, then bath").
• Offer simple choices ("red cup or blue cup?").
• Stay calm and keep everyone safe; name the feeling ("You're mad the park is over").
• Notice and praise the behavior you want to see more of.

Ask your doctor if tantrums are very frequent, very long, involve hurting self or others, or come with loss of skills.

2.4 Potty training and daily routines

Most children in the US show readiness for toilet training somewhere between about 18 and 30 months, and many are not ready until after 30 months.^[9] Signs of readiness include:

• walking to the toilet and helping with clothes
• following one- and two-step directions
• telling or showing you they need to go
• being bothered by a dirty diaper
• staying dry for about two hours
• being curious about the toilet

The AAP supports a child-led approach: wait for signs of readiness, go step by step, and avoid pressure or punishment.^[9] Setbacks during stress, illness or a new sibling are common.

Picky eating is also typical for toddlers. The AAP suggests calmly offering refused foods again (tastes change), pairing a new food with a familiar one, offering limited choices, avoiding power struggles and not using sweets as rewards.^[10]

Sleep: 1 to 2 years, 11 to 14 hours per 24 hours including naps.^[7]

2.5 Developmental concerns

Bring these up with your child's doctor (this is not a complete list):

• not meeting several milestones for their age, or losing skills they used to have
• not responding to their name, or rarely making eye contact or sharing interest by pointing or showing
• no words by about 18 months, or not combining words by 2 years
• not walking by 18 months
• you or another caregiver feel something is off

Your child should get a general developmental screening at 18 and 30 months and autism screening at 18 and 24 months.^[4] If your child is under 3, you can call your state's early intervention program directly; no doctor's referral is needed.^[11]

2.6 Resources for toddlers

• CDC checklists, 15 months to 30 months, and the free Milestone Tracker app
• Find your state's early intervention program
• AAP: picky eating
• Free from UpOnly Learning: our Essentials flashcards cover everyday words (colors, animals, numbers) in English, Spanish and Portuguese, read aloud. At this age, use them together, as a talking game, a few cards at a time.

Part 3: Preschoolers (3–5 years)

How preschoolers learn. Preschoolers learn through play, conversation, stories and hands-on experiences. Pretend play is a big part of it. Research on guided play, where a child leads the play inside a setting an adult has thoughtfully set up, suggests it can help young children learn specific content while keeping the joy of play.^[12] In Piaget's well-known framework, ages 2 to about 7 are the "preoperational" stage: children think in symbols and pictures and are learning to see things from other points of view. Modern research shows the stage ages are approximate.^[13]

3.1 School readiness and independence

"Kindergarten ready" is about much more than letters and numbers. The CDC 5-year checklist includes:^[2]

• Social: follows rules or takes turns in games; does simple chores at home.
• Language: tells a story with at least two events; answers simple questions about a book or story.
• Thinking: counts to 10; names some numbers between 1 and 5 when you point to them; pays attention for 5 to 10 minutes during activities; writes some letters in their name; names some letters when you point to them.
• Movement: buttons some buttons; hops on one foot.

Independence skills matter too: using the bathroom, washing hands, putting on a coat, opening a lunch container and asking an adult for help.

3.2 Language, "why" questions and cognitive growth

By 3, most children have conversations with at least two back-and-forth exchanges and ask "who," "what," "where" or "why" questions.^[2] Endless "why?" questions are a sign of a growing mind. Answer simply, and sometimes turn it around: "Why do you think the ice melted?"

By 4, most children speak in sentences of four or more words, say some words from a song or rhyme and talk about at least one thing that happened during their day. They name a few colors and can guess what happens next in a familiar story.^[2]

Reading aloud every day, talking about the pictures and asking open questions, is one of the simplest habits that supports language at this age.

3.3 Social skills and peer interaction

• 3 years: calms down within about 10 minutes after you leave (for example, at childcare); notices other children and joins them to play.
• 4 years: pretends to be something else during play (teacher, superhero, dog); comforts others who are hurt or sad; changes behavior based on where they are (library vs. playground).
• 5 years: follows rules or takes turns when playing games with other children.^[2]

Playdates, sharing practice and simple turn-taking games build these skills.

3.4 Behavior and emotional development

Preschoolers are learning to manage feelings, wait and follow rules. These skills are part of executive function: holding information in mind (working memory), stopping an impulse (inhibitory control) and switching between tasks or ideas (cognitive flexibility). Research suggests these skills can be strengthened with practice that gets gradually harder, and through activities such as active play.^[14] Games like "Simon says," freeze dance and taking turns all practice them.

CDC suggests clear, consistent rules, simple choices and praise for good behavior at this age, and 10 to 13 hours of sleep per 24 hours, naps included.^[15][7]

3.5 Resources for preschoolers

• CDC checklists, 3 to 5 years
• CDC positive parenting tips for preschoolers
• Free from UpOnly Learning:
  • our kindergarten readiness checklist, on the free resources page
  • free sample workbooks: the first topic of every kindergarten book, with the answer key
  • Essentials flashcards: numbers 1–100, colors, shapes and everyday words, read aloud
• Optional next step: a kindergarten Prepare summer book helps a child warm up before school starts. You'll find it in the store.

Part 4: School-age children (6–12 years)

How school-age children learn. Between about 7 and 11 or 12, children move into what Piaget called "concrete operations": they can reason logically about real, concrete things, though abstract ideas are still developing.^[13] This is the age of building skills step by step. Two of the best-supported study habits from learning research are practice testing (retrieving answers from memory) and spacing practice out over time; rereading and highlighting are much less effective.^[16] For new material, studying worked examples before solving problems alone can reduce overload and help beginners learn.^[17]

4.1 Academic development and learning

• Reading usually moves from learning to read (grades K–2: sounds, letters, decoding) to reading to learn (grade 3 and up: meaning, vocabulary, longer texts).
• Math builds in layers: number sense and addition and subtraction early, then multiplication and fractions in grades 3–5, then ratios and early algebra in middle school. Gaps in an early layer can make later work harder.
• What helps: short, regular practice; asking your child to explain their thinking; and checking what they already know before teaching something new.

If a child struggles a lot more than classmates with reading, writing or math, despite good teaching and practice, talk with the teacher and ask whether an evaluation makes sense (see school services).

4.2 Attention and executive function

Attention spans and self-control grow a lot between 6 and 12, but unevenly. Executive function skills keep developing well into adolescence.^[14] Practical supports:

• one task at a time, broken into small steps
• a regular homework spot and time, with screens away
• checklists and visual schedules
• physical activity: CDC suggests at least an hour a day for this age group^[18]

If attention problems are ongoing, show up both at home and at school, and get in the way of learning or friendships, ask your child's doctor. Only a qualified professional can evaluate for conditions such as ADHD.

4.3 Social-emotional growth

Friendships, teamwork and fitting in become more important in these years.^[18] Children start comparing themselves with others. Praising effort and strategy ("you kept trying different ways") is more useful than praising traits ("you're so smart"); research on feedback finds praise aimed at the person tends to help learning least.^[19]

Talk about school and friends often, in low-pressure moments like car rides or meals. Watch for signs of bullying (avoiding school, lost belongings, mood changes) and contact the school if you are concerned.

4.4 Sleep, screen time and daily life

• Sleep: 9 to 12 hours per 24 hours for ages 6 to 12.^[7] A consistent bedtime routine and screens off before bed help.
• Screens: The AAP now emphasizes the quality and content of media, and how it fits with sleep, activity and family time, over a single number of minutes.^[20] A written family media plan helps set expectations.
• Chores and responsibility: regular, age-appropriate jobs build independence.^[18]

4.5 Resources for school-age children

• AAP: how many hours of sleep does your child need?
• AAP: family media plan
• Free from UpOnly Learning:
  • free printable worksheets by grade and free sample workbooks: one full topic of every workbook, with answer keys
  • the free parent's math guide and parent's reading guide
  • free flashcards for math facts and vocabulary
• Optional next step: UpOnly Learning lessons follow the steps research supports: a quick check first, worked examples, guided practice, then practice alone. See how the method was built.

Part 5: Tweens and teens (13–18 years)

How teens learn. The brain keeps maturing into the mid-to-late 20s. The parts used for planning and weighing consequences (the prefrontal cortex) mature last, which helps explain why teens may take more risks, especially around peers. The teen brain also adapts well to challenge, practice and new experiences, and most teens grow into healthy adults.^[21] Teens can reason about abstract ideas, which Piaget called "formal operations," and they are working out who they are.^[13]

5.1 Puberty, physical growth and body changes

• Puberty usually starts between about 8 and 13 in girls and about 9 and 14 in boys.^[22]
• For girls, periods usually begin about two years after breasts start to develop.^[23]
• Talk to your child's doctor if signs of puberty begin before about 8 in girls or 9 in boys, or if there are no signs by about 14 in girls.^[22][23]

Growth spurts, acne, body odor and body-image worries are common. Talk early and plainly, and keep the door open for questions.

5.2 Mental health and emotional development

Moodiness is common in the teen years, but many mental health conditions first appear in adolescence.^[21] The AAP lists warning signs to watch for, especially when several appear together or last:^[24]

• big changes in mood, sleep, eating or weight
• losing interest in things they used to enjoy, or pulling away from friends and family
• a sudden drop in schoolwork
• constant worry or irritability
• use of alcohol or drugs
• signs of self-harm

What helps: stay calm and open, listen more than you talk, describe what you have noticed ("you've seemed really tired and quiet lately"), and involve your teen's doctor. If your teen talks about wanting to die, take it seriously. Asking directly about suicidal thoughts does not put the idea in their head.^[25] Call or text 988 for help (see crisis resources).

5.3 Social relationships, peers and communication

Friends and peers matter more in the teen years, and that is healthy.^[21] Interest in romantic relationships grows. Keep talking: regular, low-pressure time together (meals, drives), knowing where your teen is and who they are with, and talking through risky situations before they happen are all part of the CDC's advice for parents of teens.^[25]

5.4 Digital life and media

The AAP encourages graduated independence with media for teens, checking readiness for social media and watching for problems such as lost sleep, compulsive use or slipping grades.^[20] A family media plan that the teen helps write is more likely to be followed.

Sleep: teens need 8 to 10 hours a night, and puberty shifts their body clock later, which is one reason the AAP supports middle and high school start times of 8:30 a.m. or later.^[7][21]

5.5 Independence, decision-making and future planning

Teens build judgment by practicing decisions with support: managing money, schedules, jobs and schoolwork. Let them make real choices, talk through consequences and step back gradually. Steadier work habits and thinking about the future usually grow through the later teen years.^[25]

5.6 Resources for teens and parents

• NIMH: The teen brain, 7 things to know
• AAP: mental health and teens, warning signs
• NICHD: puberty
• Free from UpOnly Learning: our language flashcards (Spanish, Portuguese and English) work at any age, including the Essentials and the Entrepreneurship & Business words sets.

Part 6: Cross-age topics

Sleep needs by age

Recommended hours per 24 hours, naps included, from the American Academy of Sleep Medicine, endorsed by the AAP:^[7]

"Is this normal?" decision guide

This table is a starting point, not a diagnosis. When in doubt, ask.

Comparing children and managing parent anxiety

Siblings and classmates develop on different timelines, and the ranges are wide. Comparing is natural, but your child's own progress over time is the more useful measure. Tracking milestones with a checklist, then talking with your doctor about anything that worries you, is a calmer path than searching late at night. Remember that asking early costs little, and most questions turn out to be within the normal range.

Screen time and technology across stages

• Under 2: the AAP suggests avoiding screens except video chatting with family and friends.^[20]
• 2 to 5: set limits, choose quality programs made for young children and, ideally, watch together and talk about it. (The AAP's 2016 statement suggested about an hour a day of high-quality programming.)^[26]
• 6 to 12: protect sleep, physical activity and family time; choose quality content; turn off autoplay.^[20]
• 13 to 18: build independence step by step and keep checking in.^[20]

The AAP now puts more weight on what children watch and do, and on watching together, than on fixed time limits.^[20] Apps that are truly educational tend to keep a child actively thinking, avoid distractions, connect to the child's real life and involve other people.^[27]

When to seek early intervention or school services

Birth to age 3: early intervention. Every state and territory has a program. You can call yourself, and a doctor's referral is not required. The evaluation is free. If your child is eligible, services are free or low-cost, and a plan called an IFSP (Individualized Family Service Plan) is written with your family.^[11][28] Find your program at cdc.gov/FindEI.

Age 3 and up: your public school district. Call or write to your local public elementary school, even if your child does not attend it, and ask for an evaluation for special education services. A written, dated request is a good idea. If the school agrees, the evaluation is free and needs your written consent. If eligible, your child gets an IEP (Individualized Education Program). If you disagree with the results, you can ask for an independent evaluation.^[11][29] Schools also have a process under Section 504, a federal civil rights law; ask your school how it works.

Your state's Parent Center can help you through these steps.^[30]

Building connection and communication at every age

• Babies: respond to coos, cries and gestures (serve and return).^[5]
• Toddlers and preschoolers: talk, read and play pretend together; wait for their answers.
• School-age: ask specific questions ("what made you laugh today?"), praise effort, eat meals together.
• Teens: listen more than you lecture, respect privacy, stay curious about their world, and keep showing up.

Part 7: Resources and next steps

National and local developmental resources

• CDC "Learn the Signs. Act Early.", checklists in English and Spanish
• HealthyChildren.org, the AAP's site for parents (Spanish)
• Center for Parent Information and Resources
• Your local public library, which often runs free story times and early literacy programs

Screening tools and milestone checklists

• Monitoring is what you do at home: watching and tracking milestones with a checklist. Screening is a short, validated questionnaire given by a professional at set ages.^[31]
• Free: CDC Milestone Tracker app (English and Spanish, 2 months to 5 years).
• Ask your doctor about screening at 9, 18 and 30 months, and autism screening at 18 and 24 months.^[4]

Finding early intervention, speech, OT or counseling

• Under 3: cdc.gov/FindEI
• 3 and up: your public school district's special education office
• Speech-language pathologists, occupational therapists and counselors: ask your child's doctor or your insurer for a referral list
• Find your Parent Center

Pediatric and specialist referral tips

• Bring notes, examples and videos of what you are seeing.
• Ask what the next step is, and how long it usually takes.
• Ask whether you can start early intervention or a school evaluation at the same time as waiting for a specialist; you usually do not need to wait.
• Keep copies of every report and plan in one folder.

Recommended books, websites and apps by age

• 0–3: board books with faces, rhymes and real photos; the CDC Milestone Tracker app.
• 3–5: picture books read aloud daily; HealthyChildren.org preschool section; UpOnly Learning's free Essentials flashcards and readiness checklist.
• 6–12: chapter books at the child's level and just above; UpOnly Learning's free worksheets, sample workbooks and parent guides.
• 13–18: NIMH teen brain booklet; a family media plan your teen helps write.

Emergency and crisis resources

Appendices

Quick-reference milestone charts by age

What most children can do by each age (selected items from the CDC checklists):^[2]

For ages 6 to 18, development is less tied to exact months; see Parts 4 and 5.

Common parent search questions index

• When do babies sit up? Most can sit without support by about 9 months. See 1.3.
• Is it safe for my baby to sleep on their stomach? The AAP says back for every sleep in the first year. See 1.1.
• Is it normal for a 2-year-old not to talk? Many vary, but most combine two words by 2. Ask your doctor. See 2.2.
• When should I start potty training? Most show readiness between about 18 and 30 months. See 2.4.
• What should a child know before kindergarten? See 3.1.
• How much sleep does a 7-year-old need? 9 to 12 hours. See sleep by age.
• How much screen time is OK? See screen time.
• When does puberty start? About 8–13 for girls and 9–14 for boys. See 5.1.
• What are signs of depression in teens? See 5.2.
• How do I request an IEP evaluation? See school services.
• What is early intervention? See early intervention.

Glossary of developmental terms

• Milestone: a skill most children show by a certain age.
• Developmental monitoring: ongoing watching and tracking of milestones, often by parents.
• Developmental screening: a short, validated questionnaire given by a professional to see if a child needs a closer look.
• Developmental evaluation: an in-depth assessment by specialists to find out if a child has a delay or disability and qualifies for services.
• Early intervention (EI): services for children from birth to 3 with delays or disabilities, under IDEA Part C.
• IFSP: Individualized Family Service Plan, the written plan for early intervention.
• IEP: Individualized Education Program, the written special education plan at school (age 3 and up).
• Section 504: a federal civil rights law that can provide accommodations at school.
• Executive function: the mental skills used to plan, focus, remember instructions and control impulses.
• Serve and return: back-and-forth interactions between a child and a caregiver.
• Retrieval practice: strengthening memory by recalling information, such as with a short quiz.
• Spaced practice: spreading practice out over days or weeks instead of cramming.

Printable checklists and conversation starters

Before a doctor visit

• I wrote down my concerns, with examples and dates
• I filled in the CDC checklist for my child's age
• I have a list of my child's medicines and any recent changes
• I wrote my questions, starting with the most important
• I asked about developmental screening, if it is due

Conversation starters

• Toddlers: "Show me!" "What happens next?" "Where did the ball go?"
• Preschoolers: "What was the best part of your day?" "Why do you think…?"
• School-age: "What was hard today, and what did you try?" "Who did you sit with at lunch?"
• Teens: "What's something you're looking forward to?" "What would you do if a friend…?" "I've noticed…, how are you doing?"

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About this guide

UpOnly Learning publishes ready-to-teach lessons, workbooks, practice sheets and flashcards in English, Spanish and Portuguese, from kindergarten to grade 5 today and growing. We made this guide because parents ask us about much more than schoolwork. Our belief is simple: every student deserves clear lessons, one step at a time, and that starts with understanding how children grow.

This guide was written by our team with the help of advanced AI research tools, using the sources listed below. It was last reviewed on October 21, 2026. Guidance from the CDC and AAP changes, so check the linked sources for the latest. If you spot something out of date, email support@uponlylearning.com.

References

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2. Centers for Disease Control and Prevention. Developmental milestones (checklists, 2 months to 5 years). cdc.gov/act-early/milestones
3. CDC. Milestone Tracker app. cdc.gov/act-early/milestones-app
4. American Academy of Pediatrics. Developmental surveillance and screening. aap.org
5. Center on the Developing Child, Harvard University. Serve and return. developingchild.harvard.edu
6. American Academy of Pediatrics. A parent's guide to safe sleep. HealthyChildren.org. healthychildren.org
7. Paruthi S, Brooks LJ, D'Ambrosio C, et al. Recommended amount of sleep for pediatric populations: a consensus statement of the American Academy of Sleep Medicine. J Clin Sleep Med. 2016;12(6):785–786. pubmed.ncbi.nlm.nih.gov/27250809; AAP summary at healthychildren.org
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9. Toilet training: common questions and answers. American Family Physician. 2019;100(8):468–474. aafp.org
10. American Academy of Pediatrics. How do I deal with my picky eater? HealthyChildren.org. healthychildren.org
11. CDC. Early intervention: find EI contacts. cdc.gov/FindEI
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13. Piaget's theory of cognitive development. Encyclopaedia Britannica. britannica.com
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15. CDC. Positive parenting tips: preschoolers (3–5 years). cdc.gov
16. Dunlosky J, Rawson KA, Marsh EJ, Nathan MJ, Willingham DT. Improving students' learning with effective learning techniques. Psychological Science in the Public Interest. 2013;14(1). Summary: psychologicalscience.org
17. Sweller J. Cognitive load during problem solving: effects on learning. Cognitive Science. 1988;12(2):257–285.
18. CDC. Positive parenting tips: middle childhood (6–8 years). Legacy CDC page.
19. Hattie J, Timperley H. The power of feedback. Review of Educational Research. 2007;77(1):81–112. doi.org/10.3102/003465430298487
20. American Academy of Pediatrics. Screen time guidelines (Q&A). aap.org; How to make a family media use plan, healthychildren.org
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