Wonderopolis is a fairly new site that introduces a daily "wonder" that should interest children and adults.
I was particularly taken by Wonder #19, "What Would You Pack for a Trip to Outer Space?"
It would be an interesting question to think about with your kids. Adults may want to look through Mary Roach's new book, Packing for Mars: The Curious Science of Life in the Void [571.0919 ROA] prior to the discussion--your kids will think you're so smart!
In the Children's Room you'll find Mission to Mars by Franklyn M. Branley [J 629.45 BRA], an introduction, for kids, to extended space travel.