My sons two and honestly had being sleeping on his tummy since day one. I know they say it is bad but he wouldn't sleep any other way and I figure we all did it and survived so it can't be that bad. He sleeps with a pillow now and although he starts off on his back he normally rolls to his belly and off the pillow lots of times. He moves around so much that sometimes he starts at the top of the bed and ends at the foot. As long as he is sleeping fine I wouldn't worry about whey is in bed with him. By this age they know to move there heads to get air.