I know that stories are a lot less glamorous when they end with “…and then I went to bed at a reasonable hour”, but sleep is important. Since you are my children, there is a good chance that you will not be able to function on less than 7-8 hours of sleep a day, since I obviously can’t. I’m not saying that you shouldn’t have a few crazy nights here and there, but you have got to make it a habit as much as possible to get some sleep.
Lack of sleep tends to cause a lot of things for me. Indigestion, general aches, headaches, crankiness, and plenty of other unpleasantness. I also find that my motivation to accomplish even the most trivial of tasks is severely lacking. You are probably going to lead busy lives, and we all have things throughout the day that we need to accomplish, and when it comes down to it, motivation is really the key to getting those things done. Motivated people are more successful, and generally happier in my experience. Being pretty or smart or funny are great qualities, but lacking motivation, they accomplish little. And how much sleep you had the night before is a big factor in how motivated you are for the day.
Make sure you get into bed at a reasonable time, and get out of it at a reasonable time. And try to stick to a schedule as much as possible. I know that you are going to have long work weeks, or tough weeks at school cramming, but try not to make that standard operating procedure.