Is self-defense not a basic life skill?
A blade might be a better choice than a firearm for a young child though. Either a karambit or maybe a Fairbarn-Sykes Fighting Knife.
Have you considered the possibility that there are physical security threats to children besides school shooters? Kidnappers, bullies, gangs, thieves, etc...
How many of them would still want to put hands on a 7 year old if it means possibly getting their guts ripped open by the tool-wielding equivalent of a velociraptor claw?