Is ds allowed to sleep on his tummy? I've forgotten the rules.

[AliceTheCamelHasGotTheHump]

He's 9 months old.

He can roll from his back to his front.
He can sit himself up from lying down.
He can crawl.

He can't roll from his tummy to his back.
He can't get himself on to his back in any way.

I put him to sleep on his back and he flips over like a tiddlywink. He seems happy to sleep on his tum. Should he?

Yes...he will be fine. I assume he can lift his head and turn his head when on tummy.

Yes, he can lift and turn his head.