Charlie started rolling back to tummy at the beginning of this month, and now he's a pro. I actually missed it the first time. I left him playing on his back on the blanket, walked to a different room and walked back in just a few seconds later. He was on his tummy. I sat there thinking....'I left him on his back? Didn't I? Maybe I didn't? No, I KNOW I left him on his back.' So I flipped him to his back again, and sat there for a second, and he obligingly showed me how he did it. It was amazing, but it feels too early, I don't think it should be allowed at 4 months.