It isn't hard to find children's literature, but it can be hard to find children's literature that is high quality and diverse. When I took a graduate class in children's literature, these were some of the online databases that were recommended:
1) Children’s Literature Guide: http://www.acs.ucalgary.ca/~dkbrown/index.html
2) Kay Vandergrift’s Special Interest Page: http://comminfo.rutgers.edu/professional-development/childlit/
3) Links to websites of Children’s Book Awards and Notables: http://www.ala.org/alsc/awardsgrants/notalists/ncb
4) Orbis Pictus Award for Outstanding Nonfiction for Children: http://www.ncte.org/awards/orbispictus
5) Recommended Literature for Kindergarten Through Grade Twelve: http://www.cde.ca.gov/ci/cr/rl/ This one is probably my favorite. When you go, in you can customize your search so that you it will show you all of the books that talk about homelessness in a certain age range, for example. It is definitely worth bookmarking!
6) Awards and Best-of-the-year Lists from Cooperative Children’s Book Center School of Education University of Wisconsin https://ccbc.education.wisc.edu/links/links.asp?idLinksCategory=2
7) 50 Multicultural Books Every Child Should Know: https://ccbc.education.wisc.edu/books/detailListBooks.asp?idBookLists=42
As you look for some fun new books for the upcoming school year, I hope that these resources will be as helpful for you as they've been for me.