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.

Once upon a more staid time, the purpose of children’s books was to model good behavior. They were meant to edify and to encourage young readers to be what parents wanted them to be, and the children in their pages were well behaved, properly attired and devoid of tears. Children’s literature was not supposed to shine a light on the way children actually were, or delight in the slovenly, self-interested and disobedient side of their natures.

Seuss, Sendak and Silverstein ignored these rules. They brought a shock of subversion to the genre — defying the notion that children’s books shouldn’t be scary, silly or sophisticated. Rather than reprimand the wayward listener, their books encouraged bad (or perhaps just human) behavior. Not surprisingly, Silverstein and Sendak shared the same longtime editor, Ursula Nordstrom of Harper & Row, a woman who once declared it her mission to publish “good books for bad children.”