Children's Literature, Picture Book
This one is pretty straightforward. Even though The Snowy Day makes for an enjoyable read regardless of how old you are, it's clearly a picture book (as evidenced by the pictures on every. single. page.), and it's clearly children's literature. How do we know?
The main character is a young boy, and the storyline is simple and linear. The vocabulary is limited, the sentence structure is simple, and the topic—playing in the snow—is particularly accessible for young readers.
Then of course, there's the biggest giveaway of all: the fact that you're always going to find this one in the children's section.