It takes a bit to initially learn how to load, chamber a round, and disable a safety. Every new gun you handle will require relearning those things for the most part. Also, the first time you handle a gun you’ll probably be a bit intimidated by the whole experience and want someone to show you. I agree most kids would have been taught by an adult if they got so far as to shoot up a school. That said, if a loaded gun is lying around the house, someone can easily pick it up and do some damage with it without any training— at least until it is time to reload.