1988, Vicki Lansky, Fat-Proofing your Children – so that they Never Become Diet-Addicted Adults, page 62"What if your baby is a butterball? Does Fat-Proofing mean you should put your infant on diet?."
1917, in the Hunter-Trader-Trapper, volume 34, page 37:The skipper had his eye on a bunch of butterballs feeding not far from the boat. In fact there were ducks all around — though he did not tell me so.