So far the only books that remotely fit the description that I've seen have been:
Pedagogy of the oppressed
A is for Activist.
The divide between these two is massive, so I propose we build a reading list for new parents and parents that are trying to instill good lefty values into the babies.
In that case, The Lorax!!
Also, pretty much any book about sharing :)
The good news is that most kids stuff does touch on leftist themes, because leftism represents human ideals, which is what we initially teach our children before deciding "eh, never mind" when they get older. Cooperation, sharing, compassion... these things are all fundamental to leftist ideology. Thousand Acre Woods (Winnie the Pooh) sure as fuck ain't capitalist.