4 weeks old

Your baby may gurgle, coo, grunt, and hum to express his feelings. A few babies also begin squealing and laughing. Be sure to coo and gurgle back, and talk to your baby face to face. He'll enjoy holding your gaze now.

If you have things to do, your baby will still enjoy hearing your voice from across the room. And don't feel silly about using baby talk — babies are particularly attuned to this high-pitched, drawn-out way of communicating, which can actually teach your baby about the structure and function of language.