Yeah, the problem with someone that young is that they're going to act childish in any intense debate because... well... They're a child. That means that if they're right they probably won't take their win or loose the debate they won't take it gracefully but rather shove it in your face or do some major sulking. Even in the debate they're likely to turn to name calling and the like. It can easily get your back up and cause you to return the intensity back at them, probably not in a childish way but still... intense.
The only way to do it is to keep it non-serious and almost a little teasing, a lot like the old Bill Crosby show where he'd interview various kids about all sorts of subject to hear their funny responses and opinions. If you see or feel it getting intense then thats the time to find some way to turn it into something more casual or jovial.
...but yeah, sometimes the little suckers can just get to you *PMSL*
