It’s possible I’m confounding two children’s books. I remember reading this/these book(s) as a child in the 1980s. Book(s) featured a young boy who has trouble falling asleep. He wakes up or is still awake late at night, fearful of wild animals coming into his house. He is not believed by his parents. After dark he encounters wild animals, including a lion or tiger coming down the stairs of his home. He is afraid but is not harmed. I also remember (possibly from the same book or perhaps from another book) that the boy is at school, daydreaming. He looks out the classroom window and is scolded by the teacher. He sees an alligator/crocodile, who is beckoning him to go on an adventure to return the alligator/crocodile to his home. The boy travels with the alligator/crocodile through water. The alligator/crocodile says goodbye, offering the boy his tooth as a parting gift. The alligator/crocodile has a single tear on his cheek as he says goodbye. The book(s) have a dreamy, whimsical feel and I remember being frightened of the wild animals and enjoying the illustrations.