For myself, I guess it would depend on several things.
Did I recognize the kid? Have I seen him before with paintball equipment? Is it a "nice" neighborhood? A little bit rough neighborhood? Etc. If it happened in my neighborhood, I'd be more cautious. If it happened in my mom's neighborhood, I'd regret not being able to grab my paint-ball gear and go out as a lone assassin to inject some unpredictability into the game. (Meaning, it would be so likely to be air-soft or paintball, that the assumption is almost totally guaranteed to be correct in mom's neighborhood.)
We want to be a little careful that we don't scare ourselves into assuming the worst in all cases from a steady diet of self-defense and crime stories.