What working mom doesn't ache at the thought of missing her little one's "firsts"? Well, here's one you can help orchestrate: your baby's move to a big-kid bed. Just be sure both of you are ready to say so long to the crib.Children often make the bed switch between 18 months and 3 years, says Jodi Mindell, PhD, associate director of the Sleep Center at the Children's Hospital of Philadelphia. What often signals the timing: Your baby is simply outgrowing his crib. Or you're motivated by another baby on the way. Then there's the little adventurer who can't wait to climb out of his crib—and plop onto his head. "Some parents have their toddlers make the change by age two without any problems," says Dr. Mindell. But many little ones have difficulties, she adds, like continually getting out of bed when they shouldn't or frequently crying out for Mommy. "That's why I strongly suggest switching beds closer to age three, when a child can cognitively understand the boundaries of staying in bed."Still, Dr. Mindell, adds, "some children are ready younger." Yours may be a calm sleeper overall, precocious in his understanding of stay-in-bed rules or simply tall for his age. And if your child's already potty trained and needs to get in and out of bed, it's probably time to transition out of his crib. Since many toddlers don't handle change well, talk about it first and involve your child in shopping for his new bed and sheets—whether you opt for a toddler bed with built-in rails or a twin bed with an attached guardrail at first for safety.Even if your child is excited about his new bed, expect some initial angst when you leave the room. Just make sure the rails are well secured and that he has his favorite stuffed friends for comfort. Will he get out of bed to look for you? Maybe, but "don't put the thought in his head," says Dr. Mindell. Chances are he'll accept the "invisible barrier" if you simply say, "I know you'll stay in bed." And enjoy the moment, because next thing you know he'll be a teenager, and the issue will be getting him out of bed rather than keeping him in it!    Transition Tamers

These successful tactics will help you set the guidelines—not your child, says Dr. Jodi Mindell.

Give him cues to build on. Tell him how happy you are about his big-kid bed. If he's potty trained, say, "Look how my big boy got out of bed all by himself!" Stick to usual routines. Your sleeping on his floor the first few nights won'thelp him—and may mean you'll still be there four months down the road.