Do you have the kids sign the waivers, or the guardians?
I gotta say, this all sounds like a mess waiting to happen. 8 is 100% way too young. And if you're not aware of "what legal power they hold", and that's your only protection, I would highly recommend you stop allowing people on your field immediately, until you're more familiar with what consequences could rain down on you.
I have a feeling you're going to get some harsh, but straight forward replies in here, from very knowledgeable people, so I'd suggest you listen to them closely.
On a side note, one of the benefits of having older players that are often more mature, is that if you allow them to have 450FPS sniper rifles, they'll know better than to use it as a CQB weapon. Don't give a shot you wouldn't take.