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.
Yeah I never watched Korra, I was thinking it would be similar to ATLA. Nevermind that one then.
Honestly that scene and Jeff Goldblum voicing a character obsessed with money who has a large nose and a rats tail whose name is something to do with Vermin is what makes me suspect Captain Planet likely hasn't aged very well at all. But as a child, it definitely introduced me to ideas that I think set me up to be open to leftism.
Also if you want to really laugh look up the episode on the The Troubles. The IRA and the loyalists are trying to nuke Belfast and everything is solved because one guy from each side open a bakery together that I swear is Queer coded.