What is the author's style in The Phantom Tollbooth by Norton Juster?

The point of view of the novel is in the third person. As Milo is the main character, the reader is sometimes given a glimpse of his thoughts, while the other characters are only given a "voice" when they are actually speaking. A particularly notable example is Chapter 12, The Silent Valley, when all the characters lose their ability to speak in the Valley of Sound. The narrator keeps the reader informed of Milo's thoughts, but the other characters must be physically described: "The Humbug...leaped to his feet in terror, and Tock worriedly checked to see if he was still keeping time."