Kids are sponges. Not basketball, but the 7-8 year old football team I coached last fall is probably the smartest group of kids that age that I've ever been around. I started out with a basic wishbone offense, and developed it into 4 formations with 28 plays by mid season. #championship
Yep, I put in a simple 2-1-2 defense, and they played it so well, I put in a half court trap and now a full court press trap. I don't think you can put everything on them all at once, but once they have it, you can put different things to add to it.
The main problem with my team, is they are playing for the first year with me and learning everything in the 5 1-hour practices that I have had. We are playing against teams that have all played and been together for a couple of years...or at least their core group has. As the year progresses and next year as they have been in my "system" and learn what I want and learn their teammates, we should be pretty competitive...