I disagree. It is not your responsibility to keep other people from using your property illegally and immorally.
It is when you've either encouraged it or they are a minor in your care. There is no reason to presume the former, but the latter is an unanswered question. All the shacking up in this country makes this a case by case determination.
Well, it is your responsibility if the person using your property is a minor under your supervision. Since he’s probably not the legal guardian of the kid, I don’t know if that applies in this case.
it is your responsibility to keep your firearms away from children. period. it was his negligence that allowed the kid to get a hold of the gun in the first place.