"We shot each other in the foot!"
See, they had been wondering what it felt like to be shot, so they had "borrowed" a couple of their dads' guns, and shot each other. Pretty dumb, but arguably not quite as dumb as what Burress did. Plus, they had the excuse of being junior high students, a class of people not well known for their good judgment. Of course, the same could be said of professional football players...