I upvoted this but I need to reiterate my support.
When I was a kid, I was heavily into video games and had a burning desire to create my own. However, the options for doing so were not great. One of my middle school teachers tried to introduce us to programming via creating Space Invaders in perl, which went as well as you might imagine. There were a few GUI game making applications that were all terrible and extremely limited. I eventually managed to make a game using Flash, but all the overhead of arcane Actionscript APIs was overwhelming and discouraging. I stopped programming and for several years thought I was going to go into media, creating films and animation. I eventually picked up programming again in college, but there were many years of programming experience I could have had if I had stuck with game dev.
I'm convinced that if PICO-8 existed when I was originally interested in making games, I never would have stopped programming. PICO-8 is the perfect balance of easy-to-learn and powerful. Lua is a good first language because it's so small, and encourages you to build your own solutions rather than rely on magical libraries. For example, I never knew how a list-shuffling algorithm (Fisher-Yates) worked until I needed to write my own because Lua and PICO-8 don't provide one.
The limited sprite and sound options encourage you to spend time not on the assets but on the gameplay (the code). It's quick to get things on screen and working because the PICO-8 API is simple, logical, and not arcane (cough Actionscript cough).
Basically, it introduces programming in an instant-gratification way that's able to grab and hold a child's attention, while still being powerful enough to produce games that aren't hamstrung by toy programming languages.