TeachingBooks.net includes support materials about children's books, author interviews, etc.--it primarily offers literary context for books. There are 300 (or so) full audio book readings on the site--and 13,000 brief excerpts.
To find Leveled Readers in OneSearch:
1) Select Advanced Search
2) Change "Any Field" to "Subject"
3) Change "Contains" to "Is Exact"
4) Search for Readers
To find Picture Books in OneSearch
1) Search for "Juvenile Works" (in quotes)
For both types of books:
At the Search Results Page:
1) Select Resource Type--Books
2) You can also filter to Full-Text Online for Digital Only Resources
3) And you can change the Sort from Relevance to Date-Newest