Answer:
You might start with the Holocaust Museum in Washington DC; or their website (linked below). Much reference material is provided on the site.
You might read the true personal story of a little JW girl, facing the onslaught of the Nazi regime: "FACING THE LION: Memoirs of a Young Girl in Nazi Europe" by Simone Arnold Liebster (This is excellent for parents reading to their children.)
Or the story of her husband during those years: "Crucible of Terror" by Max Liebster
You may also obtain a video production by Jehovah's Witnesses: JEHOVAH'S WITNESSES STAND FIRM AGAINST NAZI ASSAULT which has been shown on Public Television; and in scholastic venues. (This can be obtained for free at any Kingdom Hall of Jehovah's Witnesses; or thru commercial sources linked below.)
Please see Links below.