I have flown on early AM flights with my boys - 2 years ago we had a 6am departure from SLC-ATL.

My tips:
1. Have the kids shower/bathe the night before.
2. Lay their clothes out the night before with everything -- including socks, shoes, and undies in one location.
3. Each kid should have a little backpack with snacks and NEW activities that they have not seen before (crayons, coloring books, those Crayola markers that only write on special paper).
4. Good ideas for snacks are granola, cheerios, string cheese, fruit snacks.
5. My kids each have a Nintendo Game Boy and they share the games; we have about 8 games.
6. If you have an iPad, download a couple of cartoon movies for them to watch on the flight. My kids love Cars for some reason. It just never gets old.
7. Sometimes security will let me take juice boxes through and sometimes not. It's worth a try, the worst thing that can happen is that they take them.