Having minors participate in your practices opens a HUGE can of worms and there are legal reasons it's not allowed. First off, most states require that ANY organization (including sports) that works with minors that they all must complete back ground checks. That would mean every member of your league and potentially volunteers. Second, just because their parents sign a waiver does not mean you are exempt from liability. Unfortunately, parents sign forms and are all excited (or not) about their child's participation until they get hurt. Then the lawsuits come out. The list can go on.