Parenting a mixed child

I am frustrated. I am a black female, very dark-skinned. my husband is white. I have twins, girl/boy, who look very much like their father. I was in the grocery store and my son was throwing a fit. I spanked him on his booty and with a firm voice told him to sit down in the grocery cart. this little old white lady comes up to me and says " you should be ashamed of yourself. what would their mother say if she saw you talking to them that way and spanking them". this lady tried to pick up MY child, assuming I was the nanny. I got so pissed. I told her I am the mother and keep your hands off my child. She looked confused. there is nothing more annoying than a random stranger telling you how to discipline YOUR child. I don't tell you lay off the donuts because she's looking a little chunky. how about you mind your business and let me handle my child. surely this woman wasn't going to pay for all the things my son damaged by throwing his fit. .....UGHhhhhh. annoyed!!!!!! any anyone had this experience????