When I was a school librarian, we called them "Everybody Books." My schools served grades Pre-K through fifth grade, and Everybody liked them. They weren't "Easy" even though the spine label sported a big E. The vocabulary could be challenging. The subject matter might be historical. They were perfect read-alouds, tremendously popular with all readers.
That's why this article in today's New York Times is so disturbing. Parents steering young kids away from picture books when that's their obvious choice? Worries that young readers won't be challenged enough to get into the best colleges? Give me a break.