For daysleeps that weren't in the sling or on me, I used to put DS on his side with rolled up small blankets against his tummy and back to stop him rolling. But at night we coslept so he was on his side, mouth on boob or head rested on boob. I think once they can lift their head it is 'safer' for them to tummy sleep. Check out Dr Sears website about tummy sleeping. Prefers to Sleep on Tummy | Ask Dr. Sears®