What if the Crumbleys knew that their kid had a drinking problem. Left him alone for the weekend with an unlocked liquor cabinet and keys to their car (assume for argument the kid was old enough to drive). He has friends over, gets drunk, goes driving with them and has a horrible accident that kills his friends and another family. No one would blink at criminal liability for the parents. They were effectively serving a minor.
But swap out a gun for booze and a mentally disturbed kid (apparently was severely bullied) who drew pictures indicating an intent to commit a school shooting and when called in to his school the parents did not disclose that they had purchased their kids a handgun recently and refuse to take the kid home for the day and we are ready to let the parents off the hook for criminal charges?
The 2nd amendment was never intended to give gun owners blanket immunity from legal liability for the firearms they own. We are fed gun rights propaganda about how it is the criminals that are the problem not the guns or the law abiding gun owners. But most criminals are able to obtain firearms that are stolen from irresponsible gun owners who do not secure their firearms in their home, office or vehicles and sold on the black market. And then there are the thousands of kids who die every year either due to suicide or accidents when guns are not properly secured in the home.
If you are going to buy your kid a hand gun, teach him how to use it, not tell his school that you have firearms at home and that the kid knows how to shoot when he draws pictures that clearly indicate he is disturbed and may be planning a school shooting because you do not want anyone to take your precious Glock, refuse to take your disturbed kid home and get counseling, and then fail to even check to make sure the Glock is still secure at home after your kid got caught essentially making a threat at school, you damn well should have some criminal responsibility. The second amendment gives you the right to own a firearm. It does not give you immunity from failing to secure the firearm and failing to make sure your kid isn't in possession of the gun when he is caught at school essentially telegraphing his school shooting.