Celestia is an amazing free software package for exploring space. Budding astronauts will love being able to zip around the solar system, jumping between planets by typing their names, and throttling off to see the milky way from out in deep space. Older kids will get much more out of Celestia than littlies, but with some parental help, even young kids will get a kick out of seeing the earth from space.
There is a huge collection of add-ons for Celestia that make it easy to add new objects to the program, so that you can populate space with real-life satellites or even spacecraft from Star Wars or your kids’ favorite sci-fi show.
Celestia may require newer computer hardware in order to use all of the features. It’s available for Mac OS X, Windows, and Linux.