Baby Surprises and Shockers

Jaw-dropper: Every morning, you've leaned over your baby's crib and there her face has been, right where you last saw it the night before. Then one day, you see the back of her head instead -- and you're as flabbergasted as if a potted plant had switched windowsills. Bingo: She's learned how to flip over, or onto her side. (For some babies, this happens closer to 4 months of age.)

What it means: This skill seems to come out of the blue because you've rarely seen your baby working on it. By day, she probably spends lots of time in someone's arms or in a seat. "But in the open space of the crib, there's plenty of room for movement," Dr. Judelsohn says. Once your baby reaches 5 or 6 months, that movement may add up to major relocation. "One morning, I didn't see my son Tyler in the crib at all at first," says Megan Colburn, a mom of two in Crown Point, Indiana. "He had inched his way across the entire crib and was hidden in a corner. My heart skipped a beat!"

Where do you go from here? To encourage your baby, try putting a toy just outside her reach when she's on the floor. But also be careful (very!) not to leave her alone on a bed or changing table.