I had been meaning to ask something along these lines myself. My son is 6, will be 7 in December. He is extremely active, whirlwind of activity, and rarely is asleep much before midnight. Sometimes, he'll be up bright and early, other times (usually school mornings!) he's later up. Like me, he is definately a night owl.
He's started going to ballet classes after school on a Monday. They only last for half an hour, but he is only participating for maybe 10-15 minutes, then says he is tired, and lies on the floor at the side. The teacher is fine about it, and is going to adapt her routine to fit around him, so he gets to learn the exercises at the start before he gets too tired. She suggested it might be a stamina thing, and that could be built up gradually.
I am concerned though, that he just isn't getting enough sleep and wondered what people thought about melatonin. Someone in this thread mentioned something else, as well. I'm in the UK and I think, that GPs here can prescribe melatonin.