I endured years of protest imposing strict sleeping routine for my kids. They must be in bed and light-out earlier than most of their friends, at least so they claim.
A recent study showed a good night's sleep, when the kid is young, will help their grades, make them more socialable, and even avoid later time over-weight.
I guess this makes sense. A good night's sleep give them more energy, to focus in class, and more participatory on the playground — that becomes higher interest in activities and exercises later.