I think they should be taught about it from Year 7 (11+), here in the UK there is too much emphasis put on the kings and queens of history which I know many kids find quite mundane. Modern history doesn't seem to be as widely taught here for some reason. I think this particular subject is incredibly relevant in relation to the global problems in todays societies around the world.
I definitely don't think it should be taught any time before 6th grade at least. Let them learn some other stuff about history before they get into that. I really don't think public schools do that great of a job with history anyways in my opinion.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.