I am a big advocate of early bedtimes for children. Not only for my own personal sanity, but also because that is how the circadian rhythms of children operate best. You can read all about it in books like Sleepless in America and The No-Cry Sleep Solution (seriously, read those books: they're invaluable). Most sources say that kids do best when they fall asleep between 6:30-7:30 pm. That is right... between 6:30 and 7:30 pm. (Mine go to bed at 7:00 pm).
And then, generally, young kids/toddlers will sleep until around 6:30 in the morning (possibly earlier, if you're my son). Oftentimes, if a child is misbehaving or having difficulty managing emotions, it could be because they are missing sleep.
This might seem kind of ironic, given that I'm an unschooler (where one school of thought might be that children should be allowed to follow their body rhythms naturally and go to sleep when and where they feel like it), but I've always found that my children need to be parented to sleep (which Elizabeth Pantley talks a lot about in The No-Cry Sleep Solution). I enjoy the nighttime ritual of stories, quiet time, and putting lullabies on the CD player. It's one of the most relaxing parts of the day.
But then, by the teen years, their circadian rhythms change and they naturally start staying up later and, thus, should be allowed to sleep in later as well. This is why schools should have a later start time for teenagers. This was talked about in the book Nurture Shock, and it cited one school that pushed start time up an hour and how their test scores improved considerably because of this.
Okay. That's it.