I think one major challenge is that the Left has a strong monopoly on "childish politics." Very simple messages like "be kind!" and "love is magic!" are things that are both appealing to children on a simple level, but also just neutral enough that they don't come across as fully Left wing. Which then slides easily in to all their various propaganda.

Inversely, Right wing is usually the politic of "harsh truths." A lot of beliefs that aren't as easy to swallow but are both necessary and unbeatable. This dichotomy is why its such an age old adage for someone to be Leftwing as a youth and then grow into being Rightwing. If you don't shove your messages too hard at a kid that'll come naturally to them, and if you do you'll end up with rebelliousness often overriding it as a lot of the current generation is showing in regards to things like gays (and 80/90s PSAs did for things like drugs).

Really, I just wish they would put effort into making something good and then the political part be secondary. Because every time its just comically bad on its own before you even factor in the politics, so why would I even bother trying to show my children? I'd have better luck explaining the politics to them in real life, and then just putting on a classic Cartoon Network show.