1. Where the Wild Things Are (1963): Max threatens to eat his mother, and while being punished, runs away to the world of the Wild Things. He stares them down, becomes their king, and decrees that a Wild Rumpus begin. But he gets homesick and goes home. The 2009 movie added some hetero-romance, among the Wild Things, not Max (Max Records). There have also been stage plays and a ballet.
2. In the Night Kitchen (1970). An amazingly vivid, scary story of Mickey, who sneaks out of his bed to a surreal night kitchen, where three chefs (all of whom look like Oliver Hardy) are making the breakfast "cake." He helps them, meanwhile wondering about where his body ends and the natural world begins: "I'm in the milk and the milk's in me."
It has been banned in many schools because the toddler is naked -- don't want five-year olds knowing that five-year olds sometimes have a penis.
Sendak's art for adults often contains penises as well, but never to be salacious, to depict vulnerability rather than desirability.