The first contact I had to actual programming was messing with Pawno scripts to make gameservers in San Andreas multiplayer when I was 12... Spent hours and hours programming with it. It started simple placing coordinates where the cars should spawn until I started to mess with more 'complicated' stuff like gates that open when player get near.
I would get some game that is popular among kids that age (minecraft?) and teach them to make simple modifications, if they like they will try to push themselfs to make harder and more complex stuff, the reward/work ratio is bigger than make a game from scratch on HTML, where there is a lot that needs to be done before getting to the "fun part".