What form of poetry or song is featured in Chapter 1 of the text and what are its contents?

The first chapter of Fantastic Mr. Fox introduces a rhyme that local children sing when they see Boggis, Bunce, or Bean. The song refers to the fact that one of the farmers is plump, one of the farmers is slender, and one of the farmers is short. The song also says that while the three farmers look different from one another, they are "equally mean" (5).