[vundercind]

The free (FOSS, I believe) program Celestia is excellent for showing kids that kind of thing.

It’s also lua-scriptable. I once created a “tour of the solar system” script that worked like a presentation (hit a button to advance to the next view) for my wife to use in her classroom, in an afternoon, never having scripted the program or written Lua before. Did a top-down view with orbital tracks, zoomed to planets, did side-by-side size comparisons, all kinds of stuff. Not hard to use, very cool. Or you can just click around the UI and use keyboard shortcuts to demonstrate quite a bit of stuff.