I'm also concerned that by more or less forcing all school employees to be pro union, they are limiting the adults that will mold children's opinions. If you are pro union then are you not most likely a progressive democrat? That's a very politically biased set of teachers and staff. Are unions being used to prevent libertarian ideas from entering the schools?
I gotta be honest, this sounds more like you want to hate the union and are just grasping for any straw you can reach.
On whether a union forces you to be a progressive liberal, no. Do unions prefer Democrats, yes. Why? Since they are the one that protect union rights.
Are they brainwashing our kids, again no. I grew up in a union school system and I honestly was not once taught anything about unions in my time. Curriculum is set by the state not teachers normally. Your over thinking this.
I've only formed my opinion after working in a non union position and a union position. Companies take advantage of there power with no union present.