"That's tasty!" (4)

(Other definitions for yum-yum that I've seen before include "Bride in "The Mikado" - appreciation of food" , "Exclamation of pleasure at taste sensation" , "One of the Three Little Maids from School - that's tasty!" , "Repetitive exclamation of pleasure at eating" , "A ward of Ko-Ko (The Mikado)" .)