astro-fiction for 7-year old

Thanks to all who relied--I will be keepoing my eyes open at the used
book store--many of thes sound interesting buit out of print (but
there's always abebooks.com).

However, i already have "Wrinkle in Time"--haven't looked at it and
didn't realize that it was science fiction. Sounds like a good start.
Thanks again,

--Darin