Not sure if this idea has been floated before, but how about capping the weight division for a TEAM?
Assume an average weight of 60kg for a 12 year old for example. (I'm 22 and only 72 kg - I was never that big as a 12-year-old)
So if you have two giant islander kids who weigh 120kg each, thats fine, but all your other players are going to be tiny.
Weight divisions for players is too simple a solution - many areas just don't have enough teams for separate divisions, and it would mean that the white kids never learn to tackle properly and the Islander kids find themselves way out of their depth playing with guys 3-4 years older than them.
With a total of 780 kg split between the 13 kids on field, that gives you maybe a couple of 90kg props, maybe an 80 kg backrower or centre and 10 other kids between 45 and 60 kg. Thats a weight differential not unlike most NRL teams. Having one or two big boppas won't give too much of an advantage, but having a team of 100kg-plus giants is a MASSIVE advantage.
Maybe this is a reason why we've been producing plenty of good backrowers and big outside backs recently, but very few skilled halves?