All three of my kids have preferred sleeping on their tummy. With my first (my DS) we persisted and kept him sleeping on his back. He's been the most troubled sleeper of the three and I wonder what it would have been like if we had let him sleep on his tummy. Both my girls we let sleep on their tummy. We knew it was not the safest position, but in reality the risk is pretty small. We did it as safely as possible and we also co-sleep. Both girls have been pretty good sleepers and from very early would have long day naps. My youngest is 9 months now and she still sleeps anywhere from 2-4 hour naps during the day (twice a day) and then sleeps pretty well at night too. My 3.5 year old and 2 year old (she turns 2 tomorrow) still sleep on their tummies most of the night, whereas my 9 month old often rolls to her side now.