I'd come up with some strange statement and the challenge was to come up with the arguments they'd make if they had to argue that. What if you had to argue that Bill Clinton won the debate?See? You could come up with some things to say, and you could have a lot of fun listening to the quasi-cogent or absurd things that would be said. Looking back on the old days with my sons, I tend to self-deprecatingly call the game crazy. Why would you encourage your children to argue persuasively about things that are not true?
What if you had to argue that it's not crazy at all? Actually, I don't think it is crazy. What the children are learning — if you handle the discussion well — is how human beings deceive and manipulate with language. It's a hands-on — brain-on? — experience with how trickery is done, how people can lie with a straight face, how something can be made to sound perfectly plausible when it's clearly dead wrong. They learn how it feels from the inside to construct lies and sophistry, so they can recognize it in others and in themselves. They learn a respect for verbal skills. They learn the power and the danger. That's an important life skill! Like all the other life skills, it can be turned to evil, but critical thinking and verbal skill ought to equip them to discover an authentic ethical foundation.
What if you had to argue that critical thinking and verbal skill lead children to an authentic ethical foundation?