I agree with your last point - the parent should definitely be charged and I like what GA is doing. I also find it a little disturbing that a poster who was an educator (has Sam said he was a special ed educator?) uses the word "retard" on here regularly. My son has a learning disability and it is BS for people to use that word.
But on to the main point - I wonder if there is a way to support a middle ground on the 2A issue you flag above - if the mentally ill kid is suspected of making a credible threat, could the guns be taken away for a period? In other words, the guns are not taken away just because the kid is mentally ill, but because he/she has threatened violence with guns.