what worked for me is to start with Game Maker from YoYo Games.

You can get started with drag- and-drop GUI blocks, but eventually move to a Basic-like scripting language. You can only make simple games but it is powerful enough for commercial 2D projects. Hotline Miami was made in Game Maker, for example.

Do not embark on managing a project for him!

The scope will be impossible and lead to disappointment. Instead, try to be a guide through tutorials and help if he gets stuck on a specific problem. Interest will wane in a specific idea and he will hop to a new one. This is fine, because the objective is to learn to have fun. Be a teacher not a producer.

This was my gateway to “real” programming, CompSci and a career.