Well, Scratch is certainly a good starting point so I would assume he wants more if he's been all over it.
There are some toys and kits available but I am not really aware if they are any good.
If my little brother would make such a request I probably would want to go with Python and an Arduino project. Robots are cool so it would pique his curiosity while basics with Arduino should be challenging but manageable. The only drawback is that it probably would require some time investment on your side.
A cheaper alternative would be directing him towards writing some simple programs in Python or Java as the only setup this would require is an IDE and it would also teach him googling for information.
I think the safety online is the biggest problem here and the only thing I can think of is to only allow some domains…
Maybe some of these suggestions sound good to you, if so I'll gladly expand on them.
Also big kudos to your approach on the matter.
Ah, haven't thought about factorio. On that matter 7 Billion Humans is a cool game that can teach the basic logic behind programming.