Why doesn't he sleep?

Last night at bed time everything went as normal, the boys went potty, stripped out of the days clothes, washed up, brushed teeth, said prayers, good night kisses and laid down quietly...and I went to bed in the next room...not another sound was heard (I have good bed goers). So why at 2:30 am was Ethan still awake....and why at 4:30 was he back up...and why won't he sleep past 9:00? Which means that at most he got 6 hours of sleep! WHY ISN'T HE AS EXHAUSTED AS THE REST OF US!?!? I think this is a symptom of ADHD but he's a happy little guy...he has to be sleep deprived though! Lane Michael can and will sleep through anything and when he's tired he goes to bed....he asks to sleep, and loves it....he's our early riser but enjoys an afternoon nap when possible! He'll be the one up with AC...as long as he doesn't try to lift the baby! LOL! The good thing is we'll all be home for the first few weeks to get into a good schedule...the boys are going back to school on September 9th and it seems so soon but hopefully we'll get lots of good time in together before then and hopefully we can find a way to get this boy to sleep!