Week-by-week library · about 4 months old
Week 16
Quick answer
What is my baby up to at about 4 months old?
This week, full-on laughs and squeals are common, and they're contagious.
What's developing
Motor
Many four-month-olds push up to their elbows or further during tummy time and hold their head steady when sitting supported.
Social
Real belly laughs and squeals of delight are common around now, often triggered by silly faces or gentle surprises.
Senses
Mirror fascination often peaks; many babies enjoy watching the moving reflection for extended stretches.
Try this together this week
- Go hunting for laughs: peekaboo, silly sounds, gentle "gonna get you" games.
- Supported sitting practice for a few minutes with pillows around for a soft landing.
- Mirror play, either a baby-safe mirror or just a moment in front of a real one together.
- Read a sturdy board book together, pointing at bold images and naming them out loud.
What parents often notice
The four-month mark is a well-known stretch where sleep patterns can temporarily shift as the brain matures (often described informally as the "four-month sleep regression"); it usually settles with time and is not a sign of a problem.
Sourced to
- American Academy of Pediatrics, HealthyChildren.org
Last reviewed by the This Week Baby editorial team.