I'd disregard people who claims your son doesn't want to code (Unless A. they know him personally and B. they've actually asked him).

I would introduce him to Udemy.com tutorials, such this one, where you learn to build a clone of the game Agar.io (www.agar.io) -- https://www.udemy.com/course/socketio-with-websockets-the-de...

I'd also search Udemy.com for the terms "game" and "3D game" and explore its catalogue of courses in the Skill Category "Game Design": https://www.udemy.com/courses/design/game-design/