My family is German Jewish and my father came over on the Kindertransport; various family members were not so lucky.
I very strongly disagree with LearnandSay that the Holocaust should not be singled out for attention - as PacificDogswood correctly states upthread, "the Holocaust is pretty unique in scale and organisation and scope". In addition, it is usually used to highlight (a) other examples of genocide eg Rwanda - eg on Holocaust Memorial Day and (b) to learn lessons from the past so that we don't just view it as the action of a few (or a few million) madmen, that could never be repeated or prevented, but instead understand it as something that happened because normal, rational but unquestioning people who were afraid or wanted an easy life went along with it (as well as some psychos, probably). It's about how all of us should strive to stand up for what is right even if it is not popular or easy, and protect the weak or defenceless. It's about bullying on a grand, national level, and what happens when this is allowed to get out of hand. It is and will remain relevant to all of us.
Re the OP, though, I would not feel the need to do more than a very gently intro to the fact that lots of Jews were killed by a bad German at primary school. My parents took me to Yad Vashem, the Jerusalem holocaust museum, when I was 11, and I was far too young (and sensitive). I have never forgotten it - in a haunted kind of way - and would not recommend graphic images like that for children of any age - strictly adults only. My own perspective on the Holocaust has been influenced by my father's amazingly upbeat and positive approach to his past - he knows and I know that he only survived because of a family of good Germans who risked their own lives to save him and his father on Kristallnacht - he had a few days in an attic too. Rather than focus on the flawed individuals who allowed it to happen, he focuses on the good individuals who defeated Nazism. It is that perspective that I want to pass on to my dcs - the amazing bravery and courage and effort of so many to defeat the evils of Nazism.
By the way, I find it astonishing that on the day the British headlines are full of the trial of a Neo-Nazi cell in Germany, that LearnandSay can attempt to claim that Nazis no longer exist and the Holocaust is no longer relevant. We have the rise of Far-Right parties all over Europe - Golden Dawn in Greece, the one in Hungary mentioned above, and some distinctly racist overtones in politics in many other countries, not least the UK. I see no reason to relax vigilance.
This does not, of curse, mean that other events in history are not also important - my eldest dc, aged 13, has read books about the Irish potato famine and slavery, for example - but I will not yet let her read anything too graphic about the Holocaust. She will study it at school next year - I hope it is not too disturbing (in particular having to be the token Jew, and being sympathetically stared at every time Jews are mentioned - rather wearing I should imagine...).