0 to 3 Months
Since your infant can't yet do much on his own, the best crib toys are those that are interesting to look at, with bold patterns -- like a bull's-eye -- and bright, contrasting colors (they don't have to be in just black, white, and red). When buying a mobile, consider it from a baby's point of view: The images should face him, not outward. You might also want one that plays music.
Every week or so, move the toys around (from the left railing to the right, for instance). Your baby will appreciate the variety, and he'll exercise different muscles in his neck and upper body, says Marilyn Segal, Ph.D., a developmental psychologist with the Family Center at Nova Southeastern University, in Fort Lauderdale.
4 to 6 Months
As your baby learns to bat at and then grasp his toys, he'll have fun making them "do" something, so the best options make noises or jiggle when they're pulled, squeezed, or shaken. He'll also enjoy baby-safe mirrors and fun textures.
Think twice before you put a toy with flashing lights in the crib. It may rev up your infant just when you want him to drift off to sleep.
7 to 12 Months
Now that he has greater finger control, he's able to play with his old favorites in new ways. You might also add a busy box -- he'll love pushing the buttons, turning the dials, and flipping the switches.
Buy toys that can be fixed securely to the rails -- with clamps, Velcro, or double-knotted ties, for example. Strings should be less than six inches long (to prevent strangulation). And, of course, avoid toys with sharp edges. Look them over carefully for parts that could detach and choke your baby, and hold any that make noise up to your ear to see if they'll be too loud for your captive listener.
Check each plaything every now and then to make sure it's still fastened tightly. Once your child can push up on his hands and knees, remove anything that hangs over the crib -- he could grab it and pull it down.