Jessica Aubin of Bainbridge Island, WA, was thrilled when her 6-month-old daughter, Josephine, did a complete 180 and moved two feet during tummy time. "I jumped the gun and told a lot of people that my baby was crawling," she says. "But a month and a half later, there's been no more action."

Stops and starts are totally normal. Big milestones, like crawling, require that your baby master several skills, including hand-eye coordination, leg movement, and trunk strength. Even if your child manages to do it once, it may take a little while for her to synchronize everything again. Another reason: Babies can surprise themselves
by, say, rolling over unintentionally, and that might scare them and make them hesitant to try again. And occasionally, overeager parents will call something a milestone that really isn't.

Sometimes, however, regression or very long plateaus of more than a month or so are red flags, says Lewis Leavitt, M.D., professor of pediatrics at the University of Wisconsin-Madison. So talk to your pediatrician if your baby has abandoned a skill she once perfected, like rolling over or sitting up.