With ds1, I had to stop nursing at 4 mo (so sad, I wanted to nurse a lot longer, please don't ask on the forum, PM if you want to know) so we had no word. Although, I was thinking of one. Maybe mama juice. But was told it sounded dirty.
With ds2, I call it "na-nas" (rhymes with mama), his dad calls it boobies, breastfeeding, nursing, whatever, and his grandma calls it che-ches and calls ds2 a "titty baby" which I kinda like. I'm trying to teach the milk sign, which he's kinda getting, he'll make a fist if I sign it. I sign milk say Na-Nas? DS2 makes fist, smiles, latches.