Ask HN: 9-yo son wants to build a game, I'm lost. What can I do?

I think you should use a platform with immediate results like this and forget about coding. There is also dreams on ps5 which is great. Try to find a way to scripting or modding a game he loves. It is really rewarding.

Also, talk about it when you are with him, in commute, at dinner...

Means, you teach them how to get back to the working start state. Then you check out the repo: https://github.com/topics/2d-platformer-game

And you help him to modify it. Add and expand it. Modding is the way to get into gamedev, without the demotivating problem of having nothign to play and long workhours without reward at the start.

Well, I as a child (say: 6-8 old) was really rather thinking deeply how a suitable way (what programmers would call "data structures" and "programming abstractions", "design of a programming languages" - but of course on a child's level) might look like so that the computer can "understand" and precisely execute my game ideas; my games as executable files would rather be the central side product of this.

I also (I am really not lying or boasting!) was thinking as a child (just to be clear: this was my child's imagination; from my present knowledge I know of no suitable way to make this actually work) how if the abstractions are there, one could easily "combine" existing games to make new games - perhaps even partly automatically by a computer:

Imagine this: using some photo editor, you can use the magic wand or lasso tool to select some part of a photo, and copy-paste this part into another photo. Why isn't it possible, if you, say, wrote both a space shooter game and an economic simulation game to select and copy-paste some part of the latter into a former to turn the space shooter into a space shooter that also contains economic simulation aspects?

The "best actually existing" (really bad) approximation of this that I have seen in life is how the GURPS tabletop role-playing game system (https://en.wikipedia.org/wiki/GURPS) enables (in principle) to "copy-paste" elements from one role-playing setting into a whole different "incompatible" one (but it is not that you would want to do this for your typical role-playing session :-) ).

Yes, this is how a 6 to 8 years old child (the former me) thinks about game development. :-)