When I was a kid Lego mindstorm was the shit but I don’t know if Lego even sells that anymore. But my advice is find some robot kit with a building block scripting language.
Alternatively download unreal engine 4, learn how to use blueprints and show them how to make simple games, as that is another “building block” scripting language.
Edit: oh, not “from scratch”, “using Scratch” haha oops. My bad.