I don’t think the problem is guns. In this particular case, there must have been some big family issues. I say family issues and not just issues with the kid because I think any parent should worry if their kid decided to start up an arsenal of pellet guns, with a real one thrown in. If that doesn’t disturb the parents or if they didn’t know about it, then there are some huge problems there.
I was brought up to respect guns. I was taken to shooting ranges many times as a kid, but safety and respect where highly stressed. With proper education and a caring family, I think it is easy for a kid to distinguish between shooting a real gun and playing with cap/water guns with their friends.