After reading lots of stories with embarrassed moms, I really really really didn't want DS shouting "boobie!" or something like that in public.
We started calling nursing "mommy milk" waaaay before DS was talking.
Before DS was talking, he used the ASL sign for "milk" (fist opening and closing).
When he got verbal he said "mommy milk".
(We call breasts & nipples by those names. So DS will happily explain that mommy milk is in mommy's breasts and comes out from the nipple. I just prefer to use "real" names for body parts.)