Could be worse. I once had to do an hr overnight layover in Narita with an 8 year old. Luckily it wasn't so bad. We found plenty to look at around the airport, and then I let him sleep right next to me while I did some work on my laptop. I did catch a few hours of sleep, so that was good too. Not ideal, but doable, eh? It does help that Japanese airlines have the best service in the world once you get on.

Anyway, good luck!! If nothing else, you'll get some good book reading.