Help her out!

From my inbox:

I just found out that I'll be teaching a third grade science fiction literature unit next year.  I'm really excited, but most of the books I can think of are for an older audience.  (I did this unit 2 years ago and the books need a serious upgrade.  But to give you an idea of the level, the one that I'm going to keep is Fat Men From Space).

I'm sure you're busy, but if you have a moment, could you recommend some titles or some resources to me?

Yikes.  That's on the young end for me.  Guys?  Thoughts?