Actually we did start with Godot - but it was too much too fast and he was overwhelmed.
He mentions this in his blog post. So we ultimately stepped back and I wanted him to learn to be resourceful. I give him a series of small changes (eg: write a function in any language that displays "hello world" on the screen) and he delivered those results in JS (he already knew HTML/CSS at this point). The rest comes as a natural progression.
I guess in this case, the best and pragmatic option was to use what you know.
In the future, we'll try Godot again :)