Because the ugly truth is that Communism KILLS. And that is an unpleasant message to bring to children. That their educators are LYING to them to usher in great strife and revolution.
If you want the “kid friendly” version, read them the story from Aesop of the Ant and the Grasshopper.
The Grasshopper knew that winter was coming but played and slacked off while the ants worked hard and saved for the future.
Read them the story of the three little pigs.
Collectivism brings everyone down to the same lowly level.
Show them the 1950s animated version of Animal Farm (which still received an “adults only” 16+ X rating in England in the 1950s as did the Wild One). It informs them that those who preach ‘equality’ do not often say that “some are more equal than others” as their hypocrisy is exposed.
I think there should be a campaign to do comic or animated versions of The Gulag Archipelago or similar stories and circulate them by any means possible. Make them into Flash games. Take aim at other sacred cows of the left as well. The disapproval of the teachers and TPTB can be the best advertising.