I don’t think an 11 year-old child necessarily needs to know about Auschwitz yet. JMHO. A 16 year-old should know, though...
These are fifth graders in the States. I think every child that age should know at least some of what happened during the second world war. There is an age appropriate book my daughter read for the fifth grade called Number the Stars. It is not gruesome. It deals with a family escaping to Denmark and then leaving Denmark when the Germans took over. It is the perfect opening for a much needed discussion. Children can handle this information and need to be taught it. You add the graphic details as they get older