I think you’re underestimating 12 year olds if you think they don’t already have a pretty good idea. I know I and all my classmates knew about death camps by the time we were in 8th grade.What you consider to be or not be appropriate for a 12-year-old is a matter of opinion. I believe the horrors of the Holocaust should be taught only when students have reached a level of maturity to process the degree of evil involved.
To be blunt, any 12 year old who doesn’t know the basics of the holocaust is spectacularly ignorant, overly sheltered, or both.