The way the kids dressed, no Nike shoes, old cars, $.25 to get into the caves, those old nickel plated metal flashlights, old rotary pay phone gave it away as a flashback. Hell the fact that kids were playing outside at all and were not in their rooms texting on an iPhone is all you needed to see.
WW2 was over in 1945 and most soldiers were home in a couple years (massive drawdown of the army, airforce, and navy). While 300K people ended up in the service from TN during WW2 there were many deferments for hardships and farming (especially 38-44 year olds). The people who showed up to hunt for the kids seem to have been farmers mostly and older.