What you say by actions, then, is that America is already the land of the not-free. Would you tell them that, outright, as well, so they would know the reason to just keep quiet? Would you tell them that America is too dangerous a place to actually speak the truth?
What I would say is, “this is an issue we as a family care deeply about. Your mother and I will be going to talk to our representatives to discuss it on behalf of the family. We’ll let you know how it went when we get home, hang out with Granny and we will see you later tonight.” Leave your kids out of it, no good can come to them speaking out on an issue like this.