If they're super motivated by the 3dness, Id suggest try Spore with the Galactic Adventures. Spore is a great 3d editing program for someone to get introduced t

If they're super motivated by the 3dness, Id suggest try Spore with the Galactic Adventures. Spore is a great 3d editing program for someone to get introduced to and Galactic Adventures let's you put all the stuff you create together in a world, with basic scripting and ai, all in a very player friendly way. (Disclaimer, I worked on these)