i have heard that joint locks can be detrimental to children. i think it had somethig to do witht he fact that their ligimnets etc were not yet fully devolped and since they were still growing it was weaker and easier to injure. i belive this is why judo jr.s can't arm bar but i have not seen any documents on it so i am not sure.
I used to beat up on the loser of the classroom from gr1-7, respectively, so I guess you could say I was involved in martial arts in a limited way during those years.
yeah i had my own personal punching bag all through primary school to try out WCW moves on. i spent almost every interval sitting outside the principals office, and got a stack of "bad behaviour" slips under my bed the size of a novel :D