getting to know children's books?

Question

how would someone define end pages of a book.

Answer 1

For me, the end pages of a non-fiction book might be the index, glossary, appendix,etc.

Answer 2

Do you perhaps mean end papers? Those are the sheets of paper pasted onto the inside of the boards, joining the text block to the covers. Often they are decorated with illustrations, maps, marbling, etc.