Fight of the Tertia (1952)

Der Kampf der Tertia (Fight of the Tertia) is the story of a group of tough but sensitive German schoolboys. Upon learning that a local catskin dealer intends to buy up all the local felines, the boys organize a boycott against the man. It's a uphill climb, since the dealer has the law and the government on his side, having spread a rumor that the cats were diseased and needed to be killed off. Thanks to the boys, who aren't above a little larceny and duplicity themselves, the villain is foiled and the world made safe for meowers and mousers once more. Kampf der Tertia is based on a popular children's novel by Wilhelm Speyer.

Unfortunately the movie Fight of the Tertia is not yet available on HBO Max.