Your trusted mentor puts a gun in your hand and tells you to kill a rival. You do it, and your mentor praises you for it.
Is the problem the gun? You? Or is it the gang mindset learned by your mentor and shared with you?
The overwhelming majority of kids killing and killed with guns are associated with criminal gangs, whose leaders are actively seeking these murders. Taking all the guns on the planet will do nothing to stop adult criminals leading children to slaughter.