My pediatrician said once they can roll over from their stomach to their back, she can sleep however she wants... she told me to always put her in on her back, but if she rolls over, she can roll back... I had my daughter wearing a Snuza monitor, which helps prevent sids... it vibrates if it detects the baby is not breathing and after a couple seconds if it still does not sense it, then it sets off a very loud alarm! So I had that extra peace of mind with that!