My son is 6 months,1 week. He has been able to easily roll from back to tummy since he was 4 months old. But once on his tummy, he can’t roll back to his back. Should I be worried about this? His development has been very good so far. He can sit up unassisted for a minute and is attempting to crawl. Just confused about the rolling. Especially because the other way, tummy to back roll, is easier. He actually was doing the tummy to back roll during tummy time when he was like 2 months old. Now when he’s on his tummy he will not roll on his back.