Babies up to 1 year of age should always be placed on their backs to sleep during naps and at night. However, if your baby has rolled from his back to his side or stomach on his own, he can be left in that position if he is already able to roll from tummy to back and back to tummy.
How long does a baby need to sleep on their back?
To reduce the risk of sudden infant death syndrome (SIDS), experts recommend that you place your baby on his back when you put him down to sleep during his first year. The risk of SIDS peaks between 1 and 4 months of age but remains a threat until babies are 12 months.