Girls can't be jesters,"" says Hester's father, a jester. But when Father can't make the king laugh, Hester does, and so--she's Hester the Jester. Why not? says Father. Why not? says Mother. Why not? says the king. It's so easy that Hester decides to be a knight, and then a king. Hester's capricious role-playing jingles right along and there might be a laugh or two in the silly advice she gives to a succession of rhyming petitioners. (""My cows run dry, my children cry""; ""My dog is sick, he can't run quick."") But her final predictable decision, just to be her mother's little girl again, comes as more of a relief than a happy resolution. Thin.