The Linux command line and the permissions system are incredibly unfriendly to adults, never mind kids. Have you tried to set up a web server with PHP on a Pi? It makes no concessions at all to beginners. You might as well be setting up Ubuntu Server LTS - only it doesn't give you any clues about security.
I'd be more interested in something that updated the experience of the old 8-bit micros, which dropped you straight into a simplified programming environment, and gave you a path to bare-metal machine code if you wanted to take it.
Maybe something like a Python IDE, with a way through to Linux for expert users, but with basic extras - a web server, a mail server, a VPS that could connect to other Pi users, a few other options - pre-installed and ready to go?