I have a children's book that is bent.  It's one of those thin oversized illustrated paperbacks. 

The last time I moved, one side of the book apparently got weighed down under something, so the pages are bent. 

There is no other damage, no water damage, etc. and I can't find anything saying bent is bad, but it's kind of an odd issue.

It's really up to you.  It sounds postable, but for kids books, I personally don't post them unless they are pristine.  I don't want to disappoint a kiddo.