Maybe he can also get interested in game design! Game design is an interesting topic all by itself and there are many books to learn from :). He seems more like

Maybe he can also get interested in game design! Game design is an interesting topic all by itself and there are many books to learn from :). He seems more like the game design type from what you have said. I suggest something that is really low-code, not Unity, perhaps Smile Game Builder (for 3D) or RPG Maker (more powerful, but 2D) if what he imagines can be somewhat fitted to RPGs. Construct 3 is also quite good -- all mentioned are great tools to bring out his imagination without becoming an exercise in 3D math and engineering. When he is 12 or 13 maybe then try Unity + Bolt and then progress into Unity + C#.