Physical Development

If you've been in the habit of leaving your baby on a bed, couch, or table to kick and play, pay special attention now. Any second, he's going to roll over, if he hasn't already. Further, while some babies are content with a tentative roll now and then, others quickly turn into whirling dervishes, able to cover large distances (like the width of a queen-size bed) in what seems like the blink of an eye. For many parents, the knowledge that a formerly immobile child is now a rocking, rolling speed demon comes with a horrifying "clunk!" as baby hits the floor. To be safe, have baby play on carpets or activity mats as soon as he can push up on his arms, arch back to lift his chest, and rock on his stomach (the precursors of rolling).

Social Development

Although it's still too early for full-blown stranger anxiety, you may notice that your little one is getting picky about his company. He recognizes and is developing a strong attachment to you and the people who regularly care for him, and is curious but more reserved around others. When he meets a stranger, he'll study the new face for a long time before favoring the visitor with a smile. Once he feels comfortable, however, he'll turn on the charm, showing off his new skills and babbling happily to his new friend.

Intellectual Development

Around this time, your baby will make an intellectual discovery with far-reaching implications: He'll realize that objects continue to exist when he can't see them. This development, which experts call object permanence, will change the way he views the world. Instead of believing that you disappear each time you leave the room (to return later as a whole new version of mommy), he now understands that you've gone somewhere else and can be called back. Similarly, if a toy falls off his high chair while he's playing with it, he no longer thinks it's gone for good; instead, he'll struggle to get down and look for it.

Note: The information above offers general guidelines, but all babies develop differently, and few hit their milestones precisely when the conventional wisdom says they should. If your child was born prematurely, you may want to use your due date as a baseline for following baby's development.