nap nightmare, 10 mth old rolling onto front and crying!

[alibo]

ds has always slept on his back, or more recently on his side. at the moment when he is put down for his nap he keeps rolling onto his front, and crying. he can crawl well and roll all ways on the floor, but in his cot once on his front he won't settle to sleep. so at the moment i keep putting him back on his side and tucking him back in. should i keep doing this or just leave him ?

ds loves to sleep on his front. Head first - bum in the air - I don't know how he breathes!
But for naps he goes on his front as a prelude to standing up and howling. So I let him howl for a minute or two, then put him back down on his side and see if he drifts off. It takes about 3 or 4 times of this before he knackers himslelf crying and nods off.