Symbolism, Imagery, Allegory
Dreams play an awfully important role in The Wee Free Men because they make up the whole of Fairyland. The Queen's world is made entirely of dreams rather than reality—she dreams up how she wants the world to look, and traps people who enter Fairyland in bizarre dreams that they cannot escape. Here is a moment when Tiffany is trying to find a way out of a dream:
She thought she heard her brain creak with the effort of thinking. If she was in a dream, she had to wake up. But it was no use running. Dreams were full of running. But there was one direction that looked… thin, and white. (11.77)
The Queen's dreams trap people. And while Tiffany is a fast learner and quick and creative thinker (as evidence by her ability to get out of dreams), people like Roland and the Queen get stuck in them for ages, content to wander around without looking for a real way out. Because of this, one of the things dreams draw our attention to as readers is how people react to them—which means that dreams are our ticket to very real character trait understanding.
Whether pleasant or horrifying, Tiffany consistently identifies dreams as unreal—even when a dream lands her back in her own home. Tiffany understands that she can't stay in a dream world forever:
"I'll wake up when I go through the door," said Tiffany, pulling Roland out of the boat. "I always do. It must work. This is my dream." (12.136)
Tiffany knows that she has to wake up in order to do real things, and to live a real life—that's why she's so adamant about all of them escaping Fairyland at the very end. Even though she's figured out a way to manipulate the dreams herself, she doesn't want to stay there. She wants to go home.