Dachau strikes me as a place that can be "scaled" down for younger middle schoolers. It would almost be possible to go to it as a memorial park. It does have some exhibits that explicitly express the gruesome truth of what went on. But those, with a little discretion and reconnaissance, can be given a wide berth as appropriate depending on the intensity level desired by the parents.
At Dachau, you don't find rows and rows of barracks. You find wide open acreage with discrete outlines in the gravel where barracks once stood. This large expanse is mostly surrounded and interspersed with monuments, memorials and chapels as testament to what went on within the camp.
The historic buildings that exist seem to capture the essence of this camp was about without a macabre focus on it.
Going to Dachau has changed my perspective on a number of things. I have been three times over the last 40 years and I look forward to going back next month with my wife and two daughters. My wife of 33 years has never been. My 26 y.o. daughter went with me about 4 years ago and my 23 y.o. daughter (who has been to Auschwitz and other Polish sites) has never been.