i deliberately have my baby sleep on her tummy since 3 months old, coz i don't want her to have a flat head, besides, she sleepsmuch better on the tummy anyways. just remember to remove all toys, towels from the crib, and don't wear too much clothes for him/her, coz heat is one of the reason for baby to suffocate in sleep. i don't know about your baby, but mydaughter moves her head freely from side to side with no problem. so you might want to monitor a bit more.