The Question and Answer section for The Poems of William Blake is a great resource to ask questions, find answers, and discuss the novel.
There is a little iambic, some anapestic with stressed and unstressed syllables thrown in for some fun. The rhyme scheme also adds to a flow that gets the “sing song” vibe you are referring to. The rhymes are really all over the place like “dark”...
"Song of Innocence and Experience" is a compelation of poems, not just one poem.
Are you referring to a specific poem in particular?