A normally growing child smiles back (social smile) at the following age
SOCIAL AND ADAPTIVE MILESTONES:
2 months: social smile(smile after being talked to).watches mother when spoken to and may smile.
3 months: Recognizes mother, anticipates feeds.
4 months: Holds rattle when placed in hand and regards it. Laughs aloud. Excited at the sight of food.
6 months: recognizes strangers, stranger anxiety. Enjoy watching own image in the mirror, shows displeasure when toy pulled off.
9 months: waves bye bye
12 months comes when called, plays a simple ball game. kisses the parent on request. Makes postural adjustments for dressing.
15 months: jargon, starts imitating mother. 
18 months: copies parents in tasking, dry by day, call mother when he wants potty, points to three parts of the body on request.
2 years: ask for food, drink, toilet, pulls people to show toys.
3 years: shares toys, know full name and gender, dry by night.
4 years: Plays cooperatively in a group, goes to the toilet alone, washes face, brushes teeth. Roleplay.
5 years helps in the household task, dresses, and undresses
6-8 weeks
4-6 weeks
2-4 weeks
6-10 weeks