Children's Books in Spanish
When I was first learning Spanish, I found children's books to be pretty useful. I bought a few but I just found either a better way or at least a cheaper way. There is a site called Children's Library where lots of children's books are available on-line for free with quite a few in Spanish.
If you use this query you will be taken to a page in English that offers the books they have that are in Spanish. There are 173 entries returned by this query.
If you happen to have a Spanish speaker in your family that wants to learn English, this query will return a page in Spanish pointing to 487 books in English.
Note that there are lots more options as far as site language and book language. All in all, a pretty useful site -- even for children. :-)