As the mother of 5, I have learned that when it comes to the subject of sleep, different children need different approaches. Just as, food-wise, there are three-meal-a-day folks and all-day grazers, my kids vary from highly scheduled sleepers to serial siesta-takers. I make sure that, whichever they are, they do have a set wake-up time. I also make sure they know how to take 20-minute recharging naps. As to bed-time, they are free to go to bed when they are tired. I do admit to making late nights boring, and turning lights off throughout the house at a set time (coinciding with my own bedtime), but they are free to stay awake all night long, if they choose, provided they are up and ready in the morning at the pre-set time.
Now, before you call this method something akin to child abuse, consider this: 1) Every child will be eager to try to stay up all night, whether or not you have a set bedtime. 2) If you take the parental disapproval out of it, you take away a lot of the allure. 3) Just a few instances of being headachy and dull from staying up all night is enough to cure most kids. My kids are self-monitoring because they have tried doing it their way, and now see WHY we keep a good sleep schedule. When they are up past their normal bedtime, due to special activities, an inordinate amount of study (they are in the AP and IB programs at school, so this is sometimes the case), or because of unusual circumstances beyond their control, they can take 20 minute recharging naps the next day, if needed, to keep their energy and alertness high.
Scientists who study sleep patterns say that such a short nap can take a person through one sleep cycle, and give the benefit of several hours of uninterrupted sleep over a short period of time, eliminating the incidence of careless errors, accidents and the like. I just know from personal experience that it works for me.
So, trust your kids. Ask them questions about how they like to sleep, how much sleep they think they need, what conditions make it easier or harder for them to sleep. Give them the responsibility for at least helping to set up those conditions for themselves. Then, unless there is a big problem, let them sleep. You'll sleep better, as well!