This is probably from the mid-to-late fifties. It involved families living in what seemed to be normal, small town America of the time. But two boys found in a garbage dump or in a nearby landfill a copy of "LOOK" magazine from their time period (1955? 1957?). Their problem was that they and their families didn't recognize any of the people or events that were reported in the magazine.
The tone of the articles in the magazine matched their actual lives in that the magazine reported world events, trouble spots, celebrities, politics, and had advertisements for cigarettes and TVs, etc. but the facts were completely different. I think the magazine was a magazine from 'real' America and they were living in a 'fake' America, i.e., they had been brought up in a separate isolated environment with everything different but now had found something from the 'real' world. The tone of the story was that they were never supposed to know about any of this. Maybe, just maybe, part of it was a story about Marilyn Monroe but none of the people had ever heard of her. I can't remember much more than that but I have a nagging thought that they were part of some controlled environment experiment by the US Military.