The others have mentioned the physical needs of the tournament. I'll focus on the more intangible needs:
Keep in mind that the set of rules you use for adults may not be ideal for children. Sure, I'd like to see judges giving points only for good clean techniques, but the children, in general, aren't going to be as sharply refined, and the longer the contest has to drag on, the more likely someone could get hurt.
Decide on your scoring methods, and stick with them. It really doesn't matter if you want to use the USANKF / WKF 8 point rule (1, 2, or 3 pts awarded for each score), the AAU / USKA 3 point rule (1/2 or 1 pt awarded for each score), etc. Just make sure the system is an established one, and hold a short seminar with all of the judges / referees before you begin the kumite events.
As for judicial bias, well, it's going to happen, regardless of whether or not the competitor's instructor is on the panel of judges (kata, kumite, kobudo, etc). Some may give their own students a higher grade, some might even be more critical of their own students, and give them lower grades. Some might have a bias against one style or another, and others look for different things.
Of course, having a set of unbiased judges would be ideal, but that's not always possible, and if anything, highly unlikely. You can't really read minds, but you can, however, put together a well-rounded panel of judges, assuming that the judges are not strict adherants to the rules.
Regardless of what division, who is judging, etc., one thing for certain, is that everyone is expected to be courteous to each other. You don't have to like the other guy at the tournament. Heck, you may even be rightfully harboring negative feelings. Still, it's up to you to extend common courtesy. Violations of sportsmanship should be dealt with in the standard manner, and if someone is grossly violating the rules on more than one occasion, calling for the shikkaku (disqualify, escort them off the premises) is certainly warranted.