I let mine sleep on their tummies when they could get over and back themselves.
There was a time when they could roll onto their tummies, but not roll back and would therefore get distressed. I used to put them in a long sleeping bag, and tuck the bottom of the bag down tightly under the cot mattress at the end of the cot, so they could roll on to their side, but no further iykwim.
But when they could move freely from back to frong and back again, I left them to it.
This post has been edited by stopwhiningatme: 21/01/2013, 10:44 AM