I'm going to insert myself into a couple's very public argument about their children.
Why would you get in the middle of this couple's public argument?
I have an issue with the way they treat their children and I'm going to say something.
You shouldn't involve yourself in stranger's arguments about their children. They could be violent and direct their anger at you.
I don't care, I don't think they treat their children well and I'm going to say something about it.
I know you feel strongly for the children but getting involved in an argument between two people could go badly for you. You should encourage them to find a solution to their issues but other than that, I would leave them alone.