Not sure I agree with Wouter, a simple box rule should suffice and promote choices for the designers and the kids.
Wether we admit it or not, most kids are quite capable of making informed choices and even have "taste's" of their own which I'm not sure we need to regulate with rules.
Ultimately, that which works best on the race course will come out the winner, and I'm not sure that there is enough info or fact available here to determine what that is yet.
Aerynt