Good Night, Gorilla by Peggy Rathmann.

"Good night, Gorilla," says the zookeeper. But mischievous Gorilla isn't quite ready to go to sleep. He'd rather follow the zookeeper on his rounds and let all of the other animals out of their cages. Little night owls can sneak along with Gorilla and see who gets the last laugh in this riotous goodnight romp. Practically wordless yet full of expressive art and hilarious, adorable detail, this book from Caldecott Medal winning author Peggy Rathmann is sure to become a beloved part of children's own bedtime rituals. There is someone at the zoo making hilarious mischief you won't want to miss!