My 6-year-old isn't quite that bad, but he gets up much before he needs to as well. If they seem fatigued, of course, it's a problem, and you might need to talk to a pediatrician. But if they seem like they're getting sufficient sleep and are just waking you too early, they're old enough to understand that they need to respect your needs as you respect theirs.
So, this isn't advice on how to get them to sleep longer, necessarily, but on how to get the sleep you need to be the parent you want to be. And especially being in school full time, you need to rest. And that's *OK.*
What we do is set an alarm not to wake our boy up but to remind him of when he is allowed to come and wake us and/or run around like a maniac making all kinds of noise. If he is awake before that time, he can read or play *quietly* in his room. When the beeping starts, he can come and ask us 20 questions, demand breakfast and explain the many Pokemon cards he has developed. It makes him feel more in control than when we tried to force him to stay in bed, and it means we get more rest.