You could get a Raspberry PI (or any computer with an emulator) or a real 80s computer. Set the PI up with whatever emulator. And maybe a book like this one
Why?! Most particularly with respect to Extended Color Basic. The horror! The horror!
Why would you cripple your child, when doing the real thing is so much easier?
Build a website. Write a game. Make your own really cool alarm clock. Make a demo. Write a voice-driven app. Steer them toward something that has relatively decent bumper-rails and ecosystems. Python. React (with typescript enabled). Or a good web framework for game development. Or, let them assemble a collection of emulator games. So many cool things they could be doing.
A Pi with no less than 8GB of RAM is a marvelous adventure. (4Gb isn't really enough to run VSCode).
I was answering the thrust of his question which seemed to be aiming for a restricted retro environment that would force some kind of technical problem solving skills without allowing kids to just run Steam or something.
That BASIC book is a really excellent intro to programming for a kid.
You could get a Raspberry PI (or any computer with an emulator) or a real 80s computer. Set the PI up with whatever emulator. And maybe a book like this one
https://colorcomputerarchive.com/repo/Documents/Manuals/Hard...
Getting Started With Extended Color Basic.
Or set up a normal Linux without installing a GUI.
Or set up an emulator with DOS Box.
Or install nothing but Unity/Unreal Engine/Godot on a computer and disconnect it from the internet.