Idiot parents not securing their weapons are the key culprit… Can minor even purchase a gun?

even in this narrow window, you are literally describing why it is a gun policy issue and not just a social issue. there is no obligation or requirement to securely store firearms, meaning it's often quite trivial for young people, the impulsive, or people who otherwise would not have access to a firearm to illicitly acquire them and do harm to themselves or others with them. this could be made much harder with some fairly common-sense regulations, but even those are fought against in this country even though they're pretty normal in other countries.