From The New York Times, The Children's Authors Who Broke the Rules:
The stylistic eccentricities of Maurice Sendak, Shel Silverstein and Theodor Geisel, a k a Dr. Seuss, are so much a part of the childhood vernacular today that it’s hard to imagine their books were once considered by some to be wholly inappropriate for children.
Yet these three authors — who each have a new book coming out this month in what can only be described as a Seussian coincidence (“But, see! We are as good as you. Look! Now we have new books, too!”) — challenged the conception of what a children’s book should be. And children’s literature, happily, has never been the same.
Judging by the reactions to Bumble-Ardy, some people STILL regard these books to be inappropriate for children!