Infant Development Milestones Checklist (0–36 Months, 2026)
0–36 month milestones across motor, language, cognitive, and social development per CDC and the 2025 Korean Pediatric Society — plus when to seek a consult.
Milestones are ranges, not averages
The CDC revised milestones in 2022 to "the age by which 75% of children achieve" the marker. Earlier kids may be earlier, but missing the table age means consult.
0–6 months
Domain
2 mo
4 mo
6 mo
Motor
Brief head control
Rolls over
Sits briefly
Language
Coos
Imitates sounds
Adds consonants (ba, ma)
Cognitive
Visual fixation
Tracks objects
Mirror reaction
Social
Social smile
Big laugh
Stranger awareness
No social smile by 2 mo or no babble by 6 mo → see pediatrician / developmental medicine.
7–12 months
Domain
9 mo
12 mo
Motor
Crawls / tries to stand
Walks holding one hand
Language
"Mama / dada" with meaning
1–2 words
Cognitive
Understands peek-a-boo
Object permanence
Social
Imitates parents
Waves / claps
13–24 months
Domain
18 mo
24 mo
Motor
Walks alone
Runs, climbs stairs
Language
10–20 words
2-word combos, 50 words
Cognitive
Points at objects
Sorts shapes, stacks blocks
Social
Separation anxiety peaks
Parallel play
Fewer than 5 words at 18 mo, or no 2-word combos by 24 mo → consider speech evaluation.
25–36 months
Domain
30 mo
36 mo
Motor
Stands on one foot
Tricycle
Language
200+ words, 3-word sentences
Questions, short conversation
Cognitive
Recognizes colors/numbers
Simple puzzles
Social
Plays with peers
Role play
Red flags
Age
Flag
6 mo
No eye contact, no facial expression
12 mo
No "mama / dada", no waving
18 mo
Fewer than 5 words, no pointing
24 mo
No 2-word combos, no imitation
36 mo
No peer interest, no short conversation
These are key for early ASD / language-delay screening. Korea's well-baby checkups (4, 9, 18, 30, 42, 54, 66 mo) review them.
Milestones are a 3-step tool: check → spot red flags → consult. Parents who track at home and re-verify at well-baby checkups catch developmental delays 6–12 months earlier.