Poor kid should've drawn a map.
It's cute. It's an adventure story. Harold is a little boy. He's drawn to look like he's about three, but he draws a lot better than any three-year-old I've ever met. He's drawing with a purple crayon. He kind of exists in this limbo of white space that doesn't seem to have walls or a floor, so it's like he's drawing on the wall, but then sometimes it's like he's drawing on the floor, and there's no clear division between the two. I think Harold is implicitly magical. Harold is the only thing in the book that's not purple except for the white background. He wants to go for a walk in the moonlight so he draws a moon, and then he draws a path. He draws a forest that consists of a single tree, and it's got a dragon under it. He draws an ocean to sail across. He draws a picnic with nothing but pie, "But there were all nine kinds of pie that Harold liked best."
Then he's sleepy and wants to go to bed, so he tries to figure out where he is. Eventually he realizes that he can't find his house, and he's a bit worried, but then he remembers that if there's a moon, his bedroom window is always right around the moon. So he draws the window, and then he draws a bed, and he lays in it and goes to sleep.
It's a little bit surreal. He clearly is not realistic as he's able to fully interact with all the drawings that he makes. It's a magic crayon. He's a magic character. But this is definitely something that a child could pretend to do, especially if you give them a large area to draw, or just some paper.
It's an adventure book, and it's a kind of a testament to the power of imagination, the power of curiosity and bravery. I think it's a great book. It's very simple. It has kind of a high number of pages, but they don't have that many words, and the words aren't long.