Stalag 13 was not a concentration camp, it was a POW enclosure. The two things are not the same in any real way.
I know - but I would have used the horrors of the concentration camps as an example of how bad the NAZIs were - and not the goofy characters as shown in the show.
Now that I recall - my kids did know about the camps quite a few years before their classmates. One of them wanted the Diary of Anne Frank, and then the others read it. She got in arguments with other kids that didn’t believe her when she discussed it at school. I’m guessing about fourth grade. So probably a similar age as I was while watching Hogan’s Heroes!
The Japanese POW camps were certainly much more akin to the German concentration camps, that is for sure. I recall reading the death rate in the Japanese POW camps approached 40%.