Create a river like the one Max sails down in the story. Take a long sheet of blue butcher paper and place it on the ground in your preschool classroom. Set it in a place where students will walk but that does not receive heavy traffic. Use a black marker to draw a few squiggly lines to create the ripples you would see in a river. Use clear tape to adhere the butcher paper to the floor. This allows students to cross the river just like Max.
Make the trees from Max's imaginary land, and place them on your classroom walls. Cut a long, skinny piece of brown butcher paper to make the trunk of the trees. Cut palm-like leaves out of red construction or butcher paper to make the red leaves and branches. Glue these to the base of your skinny tree trunks, and tape them to your classroom walls to create the look of the forest in "Where the Wild Things Are."
Place large-scale characters from the story on your classroom door and walls. Use the book for reference, and draw the monsters from "Where the Wild Things Are" on butcher paper. Color the monsters with markers to make them look more like the ones in the story. Keep their look friendly, not scary, due to the age of the children in your classroom.
Create name tags to place at your students' desks using the "Where the Wild Things Are" theme. Take a plain sentence strip, and write the names of the children on them. Next to their names, draw a crown like the one Max wears in his dream. Be sure it has five points. Color this yellow. Laminate the sentence strip, and tape it to the appropriate students' desk.
Finish your classroom decorations, and place fake trees or plants around the room. This creates the look of the forest-like environment that Max dreams about in the story. Scatter them in a way that does not block any important areas of the classroom, such as the board.