You aren’t American are you? Many families here teach their children to use guns. It’s considered irresponsible to keep guns in a house with children and not teach them to use them (though you should keep the guns locked up and away from them when not in use).

Also it’s really easy to shoot a gun without training if you don’t give a fuck about not wasting ammo or who or what you hit. Especially if you’re aiming at a crowd. It’s rare for school shooters to be decent marksmen, rather they just bring a gun with decent rate of fire and a ton of ammo and shoot into a crowd