Yup, my LO started rolling from back to front when she was only about 2 months old, and she always practises her skills in her sleep, so she was constantly rolling over, even in a Moses basket! Don't know how she managed that! It freaked me out at first, but I realised that there really wasn't anything I could do about it. I tried turning her back over, and no matter how many times I did she just rolled right back over again, or woke up very grouchy and took ages to be coaxed back to sleep, at which point she would of course turn onto her tummy again. I think a good rule of thumb is if they're able to roll themselves over then they're ready to sleep on their tummies. Naturally you should make sure the sleeping area is safe too as PPs said, but if possible, try not to worry too much.
Lisa - mama to Eleanor Rose 01/08 and Saoirse Lily 09/10