My DD is 8mths and a late roller. Just started and now loves to sleep on her tummy. Problem is she gets stuck against the side of the cot so I have to get up and move her! I really suggest getting a muslin sleeping bag tho as it will be very strange bub having his legs out. They change so much in the first year physically and mentally that it's a tall order to ask for sleep to stay the same. They just settle and their whole world changes again!