Had this thought the other day after our gaming session.
Role playing games are great fun with children. Some folks shy away from elements like death and heavy violence. D&D is a game about fighting orcs, but it occurred to me that you could tweak it just a little, leave the dashing sword fights and magic battles in, and just cut away the death and maiming aspects.
Simple really: Rename Hit Points to "Bravery Points". This is how brave and courageous you and the bad guys are. When reduced to half, or Bloodied, call it "Shaken" or "Scared". And then when the points are all gone, they drop their sword and flee the battle.
Same is true for the players. If they're reduced to 0, they're going to try to run away. If you wanted to stick close to the mechanics, change the death and dying mechanics to a terrified and fleeing mechanic. Between 0 and negative "Scared" points, they are petrified with fear, and cannot move or attack or act at all, other than making a save. In regular D&D its the stabilizing save, to keep from dying. In Kids D&D, its to keep from running as fast as you can away from the fight. Your other party members can still "heal" you as normal, though everything becomes inspiring or making people brave, or what have you.
The descriptors for everything change. It becomes PG or G rated sword fights, with clashing blades and diving out of the way, and narrow misses.