Here are 2 websites to help search for books for your child:
Scholastic Reading Counts e-Catalog Click on the "Browse Book Expert Online" icon and you can search by grade level, topic and reading level. This resource will only search books that are published in their catalogs, but it will give you titles and authors that should be available in the libraries or most book stores. (in Spanish) (in Arabic)
The Lexile Framework for Reading also has the Find a Book search tool that can be searched by grade level, topic and reading level. (in Spanish) (in Arabic)