0 to 3 months
Time on the tummy (tummy time), a few minutes at a time, helps strengthen the neck and shoulders — always supervised and while the baby is awake. High-contrast objects (black and white) catch the baby's attention because their vision is still developing. Talking, singing and making faces up close helps build a bond and stimulates hearing/vision.
4 to 6 months
Soft toys that fit in the hand encourage the baby to reach and grasp. Mirror play (the baby doesn't recognize themselves yet, but is interested in the reflection) and songs with repetitive gestures also help at this stage.
7 to 9 months
Simple peekaboo (covering your face with your hands and reappearing) helps develop the idea of object permanence. Stacking cups or large blocks, even if they knock everything over right after, is already real play at this stage.
10 to 12 months
Cause-and-effect toys (press a button and something happens) are a hit. Encouraging crawling and first steps with support (furniture, adults' hands) helps motor development.