If the person brings up family first in the middle of a discussion, then it is ok for the other person to comment on the family. Cheney was not on stage with Kerry, so therefore it was not ok for Kerry to mention his family.
It is just that simple.
Please. That seems a little bit too post hoc of a ruling to me. Cheney didn't mind when Edwards brought it up. Lynn Cheney has always acted a little wacko on this issue. Maybe this will help bring to light her past on this and her strange behavior in government, too.
And what was Cheney's response to it? He told Edwards "Thanks," and he did not continue on with the remaining time he had available to respond to the issue. He did a very classy move without slamming Edwards on the stage.
However, I go back to what I said before, Cheney wasn't on the stage with Bush, so Kerry should not have brought her up. The rest of his answer was appropriate. He only threw in that first line regarding Cheney's daughter as a tool to show that Bush and his VP disagree on a very hot topic.