Some of the rules that we use, or have used in the past are:
* No back-court count
* No 5 second closely defended count
* 5 seconds instead of 3 and encourage refs to talk the players out of the key
* Smaller ball (size 5 instead of 7)
* No zone - this is controlled by the administrators, not the referees. although refs can lodge a report at the end of games informing administrators that zone was played.
* No backcourt press
* Shoot free throws from halfway between free throw line and bottom of dotted circle
I think the most important thing to have for competitions in this age group is experienced referees. We have a referee that has been doing this age group for well over 25 years (he is 70 years old - check out an article about him at
http://www.manlybasketball.com.au/refs/). These sort of referees can take on a coaching role, explaining rules and why a player did something wrong. With the right refs, this can work really well.
Hope that I've helped, and good luck with it - you may be responsible for discovering the next Magic or MJ!