Just my two-cents, but in this militaristic world we live in, children shooting guns at things for fun during a show doesn't seem like a good idea.
I know, it's just ballons, and we're all enlightened people, and we can wrap our minds around it properly, but you never know who's in the audience, and what their experience with guns has been. I would avoid using guns in a show, period, especially for children.
Perhaps in an adult, story-telling style if you're going for a very specific mood and atmosphere, but even then, it must be carefully approached.
Call me skittish, but I want to be hired back.