Joel Schechter in Haaretz:
The discomfort caused by some of the stories – Sendak's deployment of monsters and brutes only a child can tame – may be part of their attraction. Other Sendak stories of homelessness and kidnapping, and his modern equivalents of Brothers Grimm barbarisms, could keep a child awake, too, as the books explore childhood fears in a universal picture language. But the innocents in the stories survive, and even thrive on challenges they face.
Still, there is a dark, nightmarish aspect to some of the stories, particularly for those adults who see in the visual acknowledgments of Sendak's Yiddish background images that evoke the Holocaust. “Brundibar,” with text by playwright Tony Kushner, portrays Czech Jewish ghetto children rebelling against a tyrant who resembles Hitler in an early Sendak sketch for the story. In a later draft, the tyrant turns into a clownish bully, an organ grinder with Napoleonic hat and bluster; but the story of children resisting tyranny remains a poignant tribute to its sources: Czech composer Hans Krasa's opera, and children in the Terezin concentration camp who sang about “Brundibar” in 1943 before they were sent to Auschwitz. On one level, the story is simply a fable in which children rally, sing (despite Brundibar's objections) and drive away the town bully; but it alludes to far more disturbing events of the 1940s and, as in other Sendak works, more meets an adult eye than might be seen by a child. This could explain why many of the drawings at the Contemporary Jewish Museum hang at a height more easily viewed by adults than by small children, as if the kids are not expected to see everything.
More here.