There aren't extra children. There are just those within range of the shooter. Those children or other people are the ones saved by the person with the gun who takes out the shooter. Besides, guns are not the problem. It's the bad guys, not the guns.On the flip side that just means that all those guns getting into the hands of bad guys are endangering that many extra children which is kind of the opposite to what I think the point you're trying to make is.
Woody