That's how kids are. Well... Maybe not just the kids either, here.

[He's been wandering enough to start getting the gist of what some of the enthusiastic fans are like. Ever egalitarian in his lectures, he glances down at the boy and puts on the Stern Commander face again.]

I hope you understand that you need to be careful. Real weapons are meant to be used in order to protect what's important. If you think of them as toys you'll hurt yourself and others.

[This is definitely the kind of explanation a kid is going to take seriously out of the blue, right? Right.]