Baby Developmental Milestones Guide
This guide is a reference compiled from the CDC "Learn the Signs. Act Early." 2022 revision and the Korean Pediatric Society growth-and-development recommendations. Ages are in completed months from birth. For babies born more than 6 weeks early, use corrected age (based on due date) until about 24 months.
The four domains
Development is not a single axis — it's tracked across four domains. Being advanced in one domain does not imply the same in another.
- Motor. Gross motor (head control, sitting, walking, running) and fine motor (grasping, holding a crayon).
- Language. Includes sound-making, receptive (understanding) and expressive (speaking) language. A late talker who follows commands well may still have normal receptive language.
- Social / Emotional. Eye contact, social smile, stranger anxiety, attachment, and peer play.
- Cognitive. Problem solving, cause-and-effect, object permanence, shape sorting, number and color concepts.
Key age checkpoints
| Age | Key milestones |
|---|---|
| 2m | Social smile, responds to sound, holds head briefly |
| 4m | Rolls one way, babbles, laughs out loud |
| 6m | Sits briefly, repeats syllables, turns to name |
| 9m | Crawls / pulls to stand, peekaboo, object permanence |
| 12m | First steps, first word, waves bye-bye, follows 1-step commands |
| 18m | 10+ words, points to 1-2 body parts, scribbles |
| 24m | 2-3 word sentences, stairs with rail, 1-2 colors/shapes, pretend play |
| 36m | Cooperative play, pedals tricycle, tells simple stories, draws a circle |
| 48m | Hops on one foot, names 4+ colors, draws a person |
| 60m | Speaks in full sentences, skips, tries to write name, school ready |
When to talk to a pediatrician
The signs below are conversation-starters, not diagnoses. Individual variation is large — interpret them with your pediatrician.
- 3m: No response to loud sounds or does not look at faces
- 6m: Seldom smiles or shows emotion, does not bring hands to mouth
- 9m: Does not hold head steady or sit with support, no response to own name
- 12m: Does not crawl, no babbling, no gestures like pointing or waving
- 18m: No meaningful words, poor eye contact with caregivers
- 24m: No two-word phrases or does not walk alone
- 36m: No interest in peers or cannot follow simple instructions
- Any age: Loses previously acquired skills — seek evaluation immediately
What is early intervention?
Earlier is better. In the US, each state offers free Early Intervention (0-3) evaluations and services; after age 3, services move to the school district. In Korea, public health centers, developmental rehabilitation services, and pediatric rehabilitation clinics offer assessment. Speech, occupational, physical, and sensory-integration therapies are common, with the greatest impact usually before age 3.
What parents can do at home
- Talk and read daily (15+ minutes, face-to-face)
- Supervised tummy time — short, frequent sessions while awake
- Minimize screens — under 18 months, video calls only
- Praise, eye contact, joint attention (look at things together)
- Safe exploration space — corner guards and stair gates
How to use this checklist
Pick your baby's age in months. Milestones are shown across four domains. Tick items your baby already does — checked items are marked "Achieved", unchecked items within the normal window are "Typical range", and items past the late threshold are flagged "Monitor". Use the Print button to take a paper copy to your pediatrician.
Sources: CDC Learn the Signs. Act Early. (2022 revision), Korean Pediatric Society developmental guidelines, AAP Bright Futures. Last reviewed: 2026-04-19.