2-3 Months: Social Smile
Up until now, your baby's smiles have been internal reactions to things that catch his attention. Not anymore: At this stage, he wants to connect. Your baby will smile when he sees you and will react when you make silly sounds (try mooing, oinking, and beeping). He'll also learn that he can get a reaction from you by smiling -- not just by crying. The gurgling, the grunting, the strange humming are all attempts by your baby to express himself. Now there's no question. You're his favorite. "He'll squeal and laugh when he plays with you," says Mary Ellen Renna, MD, a pediatrician in Woodbury, New York. He'll also respond to you by getting his whole body in on the act -- moving his arms and legs for emphasis.
Remember, though, that your baby won't always smile when you want him to -- and that he also has to express other emotions. But if he hasn't smiled at all by 12 weeks, tell your pediatrician so that he can check for developmental delays.