I’m not sure if these books are available in Germany, and if it’s appropriate for such a young child, but my mom used to read a series of books from Nikolai Nosov called “Neználek” in Czech with me.

It takes place in a communist society. This was my first exposure to communism, and I remember asking my father why we can’t just get houses for free, because it seems like it would help everyone… to which I got a lecture about how communism can never work, etc, you get it. I was like 5 lol

Anyway, that would be my recommendation.