I had 5 siblings. We were stair-steps - I am the youngest and my oldest sibling is only 8.5 yrs older than I am. So when we were all kids and our family walked into a restaurant, people would have that "Oh, no!" look. Fortunately, my parents had taught us good dining manners and several times we were complimented on our behavior. We never saw it as anything but a positive thing.
I work for a retail merchandiser that requires me to work in 6 NJ Walmarts a week. To say that I see/hear kids melting down or running wild in the stores would be a vast understatement; it gets old fast. So once in a while I compliment a child's behavior, not in the "Good thing you're not like the others" way, but saying how awesome it is that they're helping with the shopping (FTR, the adult is always right there with them). So far no negative responses, and I do this maybe once every few weeks. I hope a positive statement of that type is not misconstrued.