Feed me, please

So I have a question. Why is it that whenever I'm out with K and she starts crying, everyone assumes that she needs to eat. Usually they use a very self-assured statement, such as, "Oh, she's hungry," as if they are so much more attuned to my child than I. The worst came when I heard it three times in line at the grocery store, twice from the checker, who informed me that she had children of her own and knew these things, and once from the bag boy, who couldn't have been older than eighteen. Would it have helped to tell them that I fed K right before leaving the house just to avoid the very situation they were sure was at hand? Or would this just have clinched my inadequacy in their mind: "Well, if she just fed the poor dear, why is she starving already?"

On a side note, I realize now that no one ever suggests, when I am short with said checker or tailgating in traffic, that someone should feed me. In actuality, this scenario is all too common and was probably the source of K's woes in the first place. Sigh...