I need fun things to do at a sleepover for 9,10,11,12 year olds! Please answer?

Depends on whether they're male or female. I have some ideas that could be for both genders, I hope this helps you at least a little bit.
9 yr olds - board games, possibly videogames, drawing contests, flashlight tag
10 yr olds - tag, climbing trees, videogames, spitting contest outside
11 yr olds - climbing trees, makeup contest (female), friendly prank calling
12 yr olds - any combination of these should be interesting...