• Krita is free and awesome for that age. Maybe install it together. If you have a tablet or touch screen, it's really fun.
• How familiar are you with (also free) Blender? You would have to install it and learn the basics. Just the 3d sculpting program might be a blast for him and have him edit a UV sphere. There are a few basic tips to get you going, but kids pick it up way easier than adults do.
  • The object mode is for the overall, individual objects
  • The edit mode is to work on, inside, the object you select
  • You absolutely have to have a scroll mouse
  • There is a description in the lower left corner that lets you edit the mesh you're "adding" or putting in, then it goes away. This messes up a lot of people.
  • At the top are tabs that let you select a layout for Blender for each focus. There is one for sculpting.
  • The upper right has a lot of icons that let you move around the program (solid, see-thru, etc., and perspective. You would have to know this stuff.
  • This video is for you right now if you don't know anything, and for him in a couple of years: https://www.youtube.com/watch?v=uOmYInaX-wE
• Have him search Wikipedia on something he loves and to look for the sources.
• Have him look for, speed up if necessary, and learn from youtube tutorials on topics that interest him.

Side note: Affinity (photoshop alternative) just became free, but I think that's too much. Good to know about though.