Why do babies love mobiles?
By Dr. Bettye M. Caldwell
Mobiles are popular with babies because they dangle and move in intriguing circular motions. Your little one will contemplate the mobile, wondering whether the object in motion is alive, and soon, whether it's moving because baby is making it move! For the first three months you'll want to keep the mobile hanging low (8 to 12 inches over the crib) so baby can see it. After that you can begin to raise it up, keeping it safely away from baby's kicks and grabs.

By the time baby can touch the mobile it should be removed, to prevent choking on small parts or strangulation.