Vivid, Episodic, Repetitive
Oz is a strange and unfamiliar place filled with flying monkeys, a woodman made out of tin, and other things that readers have never seen before. Since Baum wrote about things that don't exist in the real world, he used extra vivid descriptions to help paint pictures in our heads. Oz itself, with its yellow brick road and Emerald City, seems to be in Technicolor, doesn't it? And notice how Baum appeals to our senses of both sight and sound in passages like this one:
The sky was darkened, and a low rumbling sound was heard in the air. There was a rushing of many wings, a great chattering and laughing; and the sun came out of the dark sky to show the Wicked Witch surrounded by a crowd of monkeys, each with a pair or immense and powerful wings on his shoulders. (12.46)
Baum was a theater man—a fan, patron, actor, and playwright—and you can see his love for drama come through in the way he writes. The chapters tend to be episodic, or self-contained, in that one Big Thing happens. For example, the book begins with a cyclone; then Dorothy's new friends are introduced, one by one; and finally those friends encounter a variety of obstacles, one at a time. Many chapters involve our friends overcoming some enemy—for instance, the Wicked Witch of the West (in "The Rescue"), aggressive plant life (in "Attacked by the Fighting Trees"), or an evil spider (in "The Lion Becomes the King of the Beasts").
All that fightin' makes for a repetitive plot structure, but Baum doesn't stop there. He also uses repetition in his sentence structure and dialogue. Dorothy repeats her goal of getting home to Kansas like a mantra—and every blessed time she mentions it, you can bet your bottom dollar the rest of the gang is going to chime in with their Amazon wishlist. Check it out:
"You promised to send me back to Kansas when the Wicked Witch was destroyed," said the girl. "And you promised to give me brains," said the Scarecrow. "And you promised to give me a heart," said the Tin Woodman. "And you promised to give me courage," said the Cowardly Lion. (15.23-15.26)
Some version of that conversation happens, oh, at least a dozen times. Repetition is a common device in both fairy tales and children's literature (and TV shows like Sesame Street, for that matter). It helps kids engage in the story because they know what's coming next.