Maybe my advice will not be popular but, I teach 3D programming professionally, and I think the best start is to stay away from code (at the beginning)! Just u

Maybe my advice will not be popular but, I teach 3D programming professionally, and I think the best start is to stay away from code (at the beginning)! Just use unreal engine, its pretty neat and powerful, it will be a very nice bounding experience to learn a (complex) software together! Don't be intimidated by all the menus, most kids at 9 can do pretty advanced stuff when they really want it. I advice to download directly a free (official) game tutorial (in unreal engine) and start to play with it, you'll have professionally made assets available, levels already designed and even some game mechanics and a step by step tutorial. When, and only when, the general procedure to make a game is understood (terrain creation, what are assets, movements, etc..) you can start with blueprints (block programming), you will be able to reach good quality games just with it. After a while (years maybe), you can start c++ ;) Note: differently than other advices, I say go directly 3d,the barrier is lower than you think with a good engine, and if he wants 3d, no need to bore him with 2d first. Note 2: A friend of mine teached 3d programming with shaders to children of 12-17 yo with great success. Note 3: some people advice Godot, I find it a neat engine, free, open-source mentality, and all that and it's very promising, BUT, you will find way less resources and community. As it's for someone young, ressources, tutorial material without code, and generally widely disponible online help is crucial to maintain a high engagement. You're not trying, at the moment, to teach him open source, but game creation, he will have plenty of time to switch if needed.