As a Soviet kid, I can assure you that there was tons of propaganda in the books that I've read as a child.

Some was pretty blatant, like the various short stories about Lenin (all adding up to how awesome he was in various respects). Some was more subtle, like the Neznaika books (https://en.wikipedia.org/wiki/Dunno) - the second one in the series was basically a communist utopia for kids, and the third one was a capitalist dystopia (that ends up with a communist revolution).

For another example, the Russian adaptation of the Wizard of Oz, which basically diverged entirely after the first book, ended the series with an invasion and occupation of Oz by mind-controlling slavery-practicing aliens (yep, the kind that come on spaceships), which ends up in a slave uprising with strong socialist overtones in the messaging.