According to the liner notes to Diamonds & Rust,

Children and All That Jazz is a phenomenon. Joan had the remnants of a tune in her head for a while, but no lyrics. She was playing around with it at the end of the session of January 22 (around 2:00 a.m.) with her new friend, Hampton Hawes. It felt good but it wasn’t exactly right, so it was decided that Larry Carlton would work on an arrangement and Hamp would come back the next night. Joan came up with the concept for the lyrics and wrote the words in about two hours the following day. Hampton matched the feat with an incredible piano solo, and Joan topped it all with three vocal tracks on the last verse.