Exactly. That's a huge part of being a kid, not understanding life through the lens of an adult. For the most part, kids don't see what we see in an equation that makes us think certain things. Sometimes, kids say and do things innocuously, and don't mean anything by it, but through an adult lens, we look at it differently because of our life experiences and adult knowledge. As a teacher of young kids, I can see a more mischievous student (likely influenced by media like movies) thinking it was hilarious to do a "funny" photo of him and big sister being "kidnapped", without realizing the implications that photo would have for adults (leading to concerns about the dangers of ACTUAL kidnapping. e.g. murder, human trafficking, rape, torture etc.).
I teach elementary school. That's called social studies. Social studies is expected and often mandated to be built into the curriculum to some capacity (arguably not enough and definitely not as much as English and math, and history is really the most dominant part of that. Kids nowadays know about WWII. It was a major historical event that kids, even young ones, may learn about in some capacity at school, reading about it or seeing it on TV, have been told about at home ("Your great-great-grandpa Rick fought in World War II in Great Britain", or whatever). Kids are smart and know a lot more than you'd expect about the past and present. Sorry, went off on a tangent there.