Max Fleischer cartoons from the 30's.
This one teaches about the brutality of capitalism and the folly of hoarding wealth: https://www.youtube.com/watch?v=AobrKFsvznY

Hey I'm not a parent but I've kinda observed my gifriends sister and her kid, so I thought I would throw in a few things.

Sesame street, as far as I can tell, is good and educational for kids. If that's wrong please lmk but from what I've observed it seems good

For older kids, adventure time is great and at the very least non-political and doesn't have cop worship. Also just an all around great show that even adults can really enjoy

Recommending against Caillou - it's a show that encourages kids to throw temper tantrums to get what they want. Very bad.

LOL this is 5 months old I'm sorry

My kids know Peace, Land, and Bread well enough to ask for it by name. The new Magic School Bus is good too. A little lib on climate change because the can’t advocate for collective and direct action on a kid’s show, but it does discuss the brutalities of climate change very well

Spongebob was pretty great when I watched it growing up. Haven't really seen many episodes past the first film release though, so I can only assume its grown stale since the original creator passed away. Mr. Krabs is probably the best representation of a greedy, parasitic, small-business owner you could ask for. Along with this it's fairly obvious to even kids that Spongebob is incredibly naive and how he gets taken advantage of, such as when he tells Patrick how lucky he is for only having to pay Mr.Krabs $50/hr to work for him, as when he started he had to pay Mr.Krabs $100/hr. Or how ridiculous it is for Spongebob to be forced to take a vacation by Mr. Krabs, ironically due to the Fry Cook Union threatening to fine the Krusty Krab a nickel due to Spongebob accumulating too much vacation time. Then of course there are simpler episodes like the reef-blower episode in which Squidward builds up existential dread having gone to live in the suburbs with people who live just like him, only to find the ceaseless monotony and conformity as even worse than dealing with the chaos induced by Spongebob and Patrick.

Adventure Time: super light and fluffy to start and ends in LGBTQ vampire romance. A non-binary main character. The overall theme is respecting others and cosmic horror.

My mother insists the reason I’m a leftist is because she let me watch Captain Planet and the Planeteers so much as a child. I’m not particularly confident that has aged well though.

When I think of the shows I really loved, they tended to be history or art based. Horrible Histories seems like a good bet based on that.

EDIT thinking more, Avatar: The Last Airbender and The Legend of Korra seem good ideas too. I also remember Recess being surprisingly left wing when I rewatched it, but I was a heroin addict at the time and don’t remember it well so I could be over estimating that.

Pingu

maybe Avatar the last airbender, you could say its a little anti imperialist and it has POC leads

You'd need to go dig through the channel and find specific videos, but if you want something explicitly leftist, the YT channel NonCompete has a number of videos with puppets to explain leftist concepts. It's been a long time since I've watched any of them, so can't comment on how kid friendly the language might be, but this is the first thing that jumped into my head.

It is also most likely pretty far off from what you're looking for.