My 4 year old has worn pjs (cotton 2-piece type) to trader joe's many afternoons after his nap. I agree, not worth fighting about. When he's done it, he usually gets a lot of attention from the workers while he's pushing his little cart walking around in pjs! He actually hasn't done this too recently, used to do it more often. If you can get your shopping done, who cares what they're wearing-as long as they're warm enough, like others have said.