Originally Posted by blackcat
... books or documentaries for age 11 that look at "communism"...
I think it is great that you are helping your son find resources to learn about this topic. The survey results at this link may be of interest. The annual poll (by YouGov, UK) basically asks Americans how much they know about socialism, communism, collectivism, Marxist ideology... and how favorably they view socialism, communism, collectivism, Marxist ideology:
1) https://victimsofcommunism.org/annual-poll/
2) 2017 - https://victimsofcommunism.org/annual-poll/2017-annual-poll/
3) 2018 - https://victimsofcommunism.org/annual-poll/2018-annual-poll/
4) 2019 - https://victimsofcommunism.org/annual-poll/2019-annual-poll/
It appears that the less one knows about socialism and communism, the more attractive these ideas are.
A free, 146-page curriculum is available on the VOC website and can be downloaded by clicking on "Programs" / "Education," and supplying your email address. The curriculum is titled, "Communism: Its Ideology, Its History, and Its Legacy," 2nd edition.

Others have recommended:
- the movie version of Dr. Zhivago, although both its length and adult themes may be somewhat of a distraction from observing the impacts of the Russian Revolution. Therefore even an 11-year-old who is quite gifted may benefit from watching with an adult who would provide guidance.
- the book "Tumbleweed," by Eddie Doherty, a biography of his wife, Catherine deHueck Doherty, who escaped communism.
- the book "Confucius Never Said," by Helen Raleigh (2014), "A four-generation family journey from repression and poverty to freedom and prosperity."