There is a PBS documentary available on YouTube called ‘Memories of the Camps’. I showed it for many years to my 8th-grade history students. It’s unfinished and roughly edited but it is very powerful. Even, rough, rowdy 8th-grade boys shut up after a few minutes. Lots of nudity—piles of dead bodies nudity. And it just keeps going on. First fifty minutes or so are of Bergen-Belsen where Anne Frank and her sister died.
If you could arrange for him to see it, it might be a substitute for a trip to the museum.
“Paper Clips” (a documentary) is another good movie about the Holocaust for this age group.