I think the parents should definitely be held responsible. We've recently had a few cases in this country where the parents are indicted and convicted. Somebody has to be held responsible for this! And when a 6-year-old brings (his own!) gun to school, what else is there to do? Who is really responsible for the crime?
Anyone who gives a child a gun, as if it were a toy, or keeps their own gun where it is accessible to their children, is a moron. Maybe criminal prosecution will get through to someone else, and might actually save a few lives.