Fallout is such a great game.
How about using old smartphones connected to an array of inexpensive sensors… make a little tricorder, an app that has hundreds if not thousands of experiments, a place to put them, a community for kids to make their experiments public, and coordinate with other kids to conduct experiments across the world.
Keep it open source, encourage hackable hardware and software.
A digital scale, gps, motion sensers, a spectrograph using the cell phone camera if you add a diffraction grating, all already there…
Imagine the joy of proud nerdy parents watching their kids explore the surface of a strange new world with their new tricorder. That would make me happy.