Now that my 5-month-old is rolling over by himself, is it safe to let him sleep on his tummy? If not, what is the best way to keep him on his back?
The American Academy of Pediatrics (AAP) recommends that parents place healthy babies on their backs to sleep until 1 year of age to reduce the risk of sudden infant death syndrome. However, once a baby can roll over comfortably from back to stomach and stomach to back (this generally happens between 4 and 7 months), there’s probably no need to roll him back onto his back if he has rolled over.
You should, however, double-check to make sure that there is nothing else in the crib with him. Babies can accidentally roll into pillows, quilts, or bumper pads and suffocate.
Source: Sleep: What Every Parent Needs to Know (Copyright © 2013 American Academy of Pediatrics)