I would suggest trying a simple game framework such as Löve or pyGame (or pyglet). The former use the lua language and the latter python. I guess Scratch could

I would suggest trying a simple game framework such as Löve or pyGame (or pyglet). The former use the lua language and the latter python. I guess Scratch could also be interesting, but I think some 13 year olds may not be attracted by it's "childish" appearance.