Placing babies to sleep on their backs instead of their stomachs has been associated with a dramatic decrease in deaths from Sudden Infant Death Syndrome (SIDS).

Safe Toddler Bedding Practices For Infants

Place baby on his/her back on a firm tight-fitting mattress in a crib that meets current safety standards.
Remove pillows, quilts, comforters, sheepskins, stuffed toys, and other soft products from the crib.
Consider using a sleeper or other sleep clothing as an alternative to blankets, with no other covering.
If using a blanket, put baby with feet at the foot of the crib. Tuck a thin blanket around the crib mattress, reaching only as far as the toddlers chest.
Make sure your baby's head remains uncovered during sleep.
Do not place baby on a waterbed, sofa, soft mattress, pillow, or other soft surface to sleep.