If a kid is serious about airsoft, he will understand what he needs to do to be able to play, he will understand that he may get turned away, and he won't bitch about it. There shouldn't be any of this talk about "turning away one good apple among thousands of rotted ones"...if the kid realy is a good apple, he'll come back with his parents, who will be in posession of the airsoft guns, and will remain at the game to supervise...or he'll wait until he's 18+ and won't have a problem with it.
Changing laws around won't help anything, imho, because people always find a way around it, and because of the nature of the sport (ZOMG, gunzzz FTW!!!11!) kids will always do stupid things. Adults will too, but at least then they're doing it legally and the responsability falls on them.
The best we can do is just refuse to play with kids, refuse to sell kids our guns and remind our friends/contacts about this fact.