Mostly what Ruby said but also what I keep trying to explain. The camp was never intended to be a regular self-defense camp. Its a Hunter's camp, made for those who intend to actively seek out trouble and intercede. I think we can all agree we don't want children running into the heat of battle but would rather have it so, if they do get cornered or attacked, they know enough to keep safe.
I've already told Hermione she's welcome to attend classes geared towards adults, and I really would appreciate you and Dick creating a class specifically for children. But the camp is an entirely different story. It isn't that I don't think many of our children couldn't handle it. It's that they shouldn't have to.