I hate to butt in, but this sounds like a very bad idea to me...
I don't know exactly what you have in mind, but running around with firearms and camo outside of your own land could be trouble. Unless you have a really good place in mind where you will not run into other unsuspecting people, I'd stick to paintball.
Not to mention the fact that I was taught to never point a firearm at a person I didn't intend to hurt. I don't care if it's blanks or not, sounds like a bad practice, and one that could lead to too many unforseen troubles.
Paintballs don't hurt that bad, and the only advantage of using real firearms in your scenario is that you get to run around with a real firearm and pretend you are a real mall ninja.
So IMHO, I think you should ditch the idea, and take everyone's suggestion of the paintball. In addition, that adds an element of teamwork and competition. Hell, find one of those indoor paintball matches, I've always wanted to try that...
Then take him to the range to fire real guns in a controlled environment.