From the book:

Perhaps I should admit on the title page that this book is "By L. Frank Baum and his correspondents," for I have used many suggestions conveyed to me in letters from children. Once on a time I really imagined myself "an author of fairy tales," but now I am merely an editor or private secretary for a host of youngsters whose ideas I am requestsed to weave into the thread of my stories. These ideas are often clever. They are also logical and interesting. So I have used them whenever I could find an opportunity, and it is but just that I acknowledge my indebtedness to my little friends.