Orphan X (Nowhere Man) books are awesome! Very much what you’re looking for, but way better than Reacher Books in my opinion, and there’s a ton of them if you do end up enjoying them!
Left wing … ehh, I mean it’s an action fuck em up book series. Probably not very left wing, I don’t remember it being as such.
We read a lot of kids books that touch on the subject: Swimmy, the Lorax, Yertle the Turtle, click clack moo, and just a lot of social justice and lgbtq+ books. They don’t have to understand marxism and you don’t have to bum them out either. Kids aren’t stupid, they can understand why we dislike people like Musk hoarding wealth.
Aside from that we take the kids to [light] protests. We have them read the signs and try to plainly answer their questions.