There is a super cute book written by Mark Kelly, a retired astronaut, called
It's about a mouse that gets to go up into space with astronauts. He is the smallest of the mice, but also the hardest worker. But he wonders how he can help the astronauts on their mission. I won't spoil the story but it's very cute and my students just loved it. The illustrations are wonderful too!
I also added an app to my iPads at school for the kids to mess with called Astro App. Students can read about different astronauts and missions. They can also take a picture of themselves and suit up into a space suit. BIG HIT!
NASA has a Kids Club site complete with games and videos for kids too. *It requires some higher reading skills* for reading instructions.