The gun should have been outright outlawed.
Laws preventing youth ownership are likely not the answer. I am going to take a hunch and say that the 10 year old girl was not licensed or the owner of the gun used.
how many people die because of accident shot by toddler? may be 1-2 per occasion.
how many people die because of assault riffle?
Can someone own an assault riffle? I think yes, but make it as hard as hell as possible, e.g. 1000% tax, ownership fee every month, license, background tests, health checks, etc etc..
Just like, can I own a helicopter? sure, but it won't be easy