My solution to this problem that I've been working on for years, but still has further to go is LiveDVD linux distribution, that includes all the source code to rebuild itself (the iso image) from scratch. Add to that, a cool interaction with some NDS homebrew, including all the source and compilers needed to modify that. Currently what I have is a fedora derived LiveDVD/USB that boots a PC into an electric guitar-f/x preamp, which when combined with speakers and a guitar, lets you easily start jamming with Rakarrack. For the NDS homebrew side, I have an application that lets the NDS talk via wifi to control Rakarrack in realtime. A TouchScreenWhammyPad implementation.
For the long term goal to achieve what you described, I intend to add more simple GPL homebrew games, and a book walking a kid through the process of tweaking some little aspects of the existing games, maybe just text strings. That would get them familiar with the development process. Then maybe a complete tutorial implementing tic-tac-toe or such (from good overcommented template code of course).
If you want to check out what I have so far-
(developer build of new f11 based version will upload today, and an f12 version should be coming pretty soon)