INFANCY

2 years

Height reaches about 36 inches, around 75% greater than birth length

5 months

Birth weight doubles to about 15 pounds

1 year

Birth weight triples to about 22 pounds

2 years

Birth weight quadruples to about 30 pounds

Birth

Head accounts for about 1/4 of total body length

Birth

Legs account for about 1/3 of total body length

2 years

Head accounts for about 1/5 of body length

2 years

Legs account for nearly 1/2 of body length

First 2 years

Synapses and neural fibers increase at an extremely rapid pace

Childhood and adolescence

About 40% of synapses are pruned to reach adult level

End of pregnancy through 2 years

Glial cells multiply rapidly and myelination increases greatly

Birth

Brain is nearly 30% of adult weight

2 years

Brain reaches about 70% of adult weight

2 months onward

Prefrontal cortex begins functioning more effectively

Preschool and school years

Prefrontal cortex undergoes especially rapid myelination and synaptic formation/pruning

First year

Marasmus usually appears

1–3 years

Kwashiorkor usually appears after weaning

3–4 months

Laughter typically appears

4–6 months through second year

Angry expressions increase in frequency and intensity

Second half of first year into second year

Fear increases

After 6 months

Stranger anxiety commonly emerges

8–10 months

Infants begin social referencing

3 months onward

Infants begin using attention shifting to help regulate emotion

Birth–6 weeks

Preattachment phase occurs

6–15 months

Separation anxiety commonly increases

18–20 months

Majority of toddlers recognize themselves in mirror self-recognition tasks

Around 2 years

Self-recognition is well underway

Around 2 years

Children point to themselves in photos and use “I” and “me”

Around 2 1/2 years

Most toddlers recognize themselves in live video and reach for sticker on head

Around 3 years

Most children recognize their own shadow

1 1/2–4 years

Delay of gratification improves steadily

12–18 months

Toddlers first become capable of compliance

7 weeks

Prereaching disappears

3–4 months

Purposeful reaching appears

5–6 months

Infants can reach for objects in darkness after lights are turned off

7 months

Infants begin reaching with one arm independently

4–5 months

Infants modify grasp according to object size, shape, and texture

4–5 months

Sitting allows coordinated two-handed object exploration

End of first year

Well-coordinated pincer grasp develops

8–11 months

Reaching and grasping become well-practiced and problem-solving improves

10 months

Infants modify reaching in anticipation of next action

4–7 months

Infants prefer proper musical phrasing

6–7 months

Infants distinguish rhythmic patterns and musical structures

End of first year

Infants recognize melodies played in different keys

7–8 months

Infants identify regular syllable-stress patterns in language

10 months

Infants detect words beginning with weak syllables using sound regularities

3–4 weeks

Infants blink defensively when object approaches face

2–3 months

Scanning ability and contrast sensitivity improve greatly

0–2 years

Piaget’s sensorimotor stage

Around 1 month

Primary circular reactions begin

4–8 months

Secondary circular reactions strengthen

10–12 months

Infants solve simple problems by analogy

14–18 months

Toddlers imitate actions adults attempt even if not fully completed

Birth–1 month

Secondary circular reactions using limited motor skills occur

1–4 months

Awareness of object permanence, object solidity, and gravity begins according to violation-of-expectation findings

1–4 months

Deferred imitation of adult facial expressions occurs over short delays of about 1 day

4–8 months

Knowledge of object properties and basic numerical knowledge improve

4–8 months

Deferred imitation of adult novel actions occurs over delays of 1–3 days

8–12 months

Infants search for hidden objects

8–12 months

Infants solve simple problems by analogy to previous problems

18 months–2 years

Infants understand invisible displacement

18 months–2 years

Beginning awareness of pictures and videos as symbols develops

Newborns

Habituation and recovery to visual stimuli take about 3–4 minutes

4–5 months

Habituation and recovery may take only 5–10 seconds

Second year

Sustained attention increases greatly during goal-directed play

2 months

Infants begin cooing

4 months onward

Infants become interested in turn-taking games like peekaboo and pat-a-cake

6 months onward

Babbling begins with repeated consonant-vowel combinations

7 months

Babbling includes many sounds of spoken languages

8–12 months

Joint attention becomes more accurate

8–12 months

Infants actively participate in turn-taking games

8–12 months

Preverbal gestures like pointing and showing emerge

12 months

Babbling reflects language-specific sound and intonation patterns

12 months

Speed and accuracy of word comprehension increase rapidly

12 months

First recognizable spoken word appears

18–24 months

Spoken vocabulary expands from about 50 to 200–250 words

18–24 months

Toddlers combine two words into telegraphic speech

3 months

Caregiver–infant vocal imitation interactions become common

4–6 months

Imitation extends to social games

5 months

Infants respond to their own name

6 months

Infants understand familiar words like “Mommy” and “Daddy”

Around 1 year

First recognizable spoken words emerge

16 months

Example of underextension: using “bear” only for one teddy bear

18–24 months

Vocabulary growth often reaches 1–2 new words per day