Sorry Lon that's a real bitch. I had a guy eat a bullet at the gun range last year while I was working and I know it took me awhile to get right with it. I can't start to imagine what you and your family are going through. I'm adding your family to my prayers tonight.
The only thing you can do for that boy is love him even a little harder and try not to dwell on what happened in front of him. Someday when he is old enough to handle such selfish acts he will understand, but until then, remember he is only a child.
God, Family, Guns, in that order.