Whew... long post there Miss Nova. but great info.
Does your son want to do animation specifically? Or do you mean more generally CG and 3d modelling etc.

If your son is interested in "drawing in 3d" I'd recommend either mudbox or zbrush. These are much more "freeform" and work better with a tablet in my opinion. Maya and 3DS are both very technical and have a steep learning curve as was mentioned. Mudbox and Z, on the other hand, you can relatively easily dive in and start messing around with sculpting and painting.
Hope that helps. Good luck!