I had to give my 9 year old an impromptu Holocaust chat because they were about to watch 'The Boy in the Striped Pyjamas'. This actually pissed me off, because it's a completely inaccurate and stupidly offensive book and a worse film. It clumsily makes the point that an audience can only care about deaths when a blonde kid gets involved. Such a dreadful message, and the book itself was poorly researched, poorly written and the author involved in plagiarism scandals, I believe. I basically told him "this is a crap book. When you're older you can read better ones. And better films, too."
ANYWAY the other issue is that at 9, frankly, none of the kids were equipped to comprehend or understand the matter to any depth. "Da bad man called Itler wanted to kill Jews" means nothing to a child if they haven't been taught any background - what is "the war", what is "the Jews", what is "the economic collapse after the punitive measures invoked after WWI", what is "antisemitism", what is "genocide."
My son and I read over a history book and he cried a bit, we both did, and he 'got' it, and we talked about it in some depth, but when he went in he said most of the kids just looked blank, couldn't answer any of the questions and were confused on basic aspects, like "what's Germany".
It just seemed a bit pointless. I could teach a bunch of five year olds about the events leading up to the Vietnam War and the Fall of Saigon, or the Cambodian Killing Fields, I'd have some nice Powerpoints and worksheets, but at the end of the day are they going to actually understand, or just be sat there looking blankly at me?
You need to kind of ease into it with your basic World War II knowledge. Set a bit of groundwork so the kids have some vague sense of where the events fit into modern history. You can't just be colouring a picture of a stone age house one day and the next day be like "well, good morning kids, here's Auschwitz".
Your other point is a good one. Primary schools are really keen, it seems, on using the killings of people, especially women, as a joke. See Henry VIII. How hilarious it is that a man murders two women and multiple men for his own ends. How funny saying "heads chopped off" is. Let's laugh at the rumour Anne had six fingers. It's vile. It's depressing that this is still going on, and even bringing in modern domestic violence murders? Jesus. There's a belief that "kids love gross stuff" but we should have evolved to the point that people being murdered isn't "funny" or "tee hee yucky". I mean, one minute the deaths of the Holocaust are tragic, but the deaths in the French Revolution are hilarious? What lesson are they learning there?