On both legs of my recent try to NRT there were children on the upper deck.

All of them behaved considerably better than the loud and obnoxious grown-ups sat at the front of the cabin on the return leg who didn't shut up for the entire flight and seemingly managed to drink their own weight in alcohol before the first meal service.

Give me the kids any day.

(actually that's not much help to the original poster... let me edit on a proper response).

I think as a child I would have gone stir-crazy if I was sat in the middle seats down-stairs with no window. However if you've got the kind of kids that don't mind that kind of isolation and will entertain themselves with movies then it's probably ideal. The only other downside is putting your kids somewhere they'd have to climb over someone's legs to get out of the seat - maybe try to find a seat where that's not necessary, or put yourself in the appropriate seat (which isn't the adjacent one of course).

But if you think you'd all be happier upstairs, go for it. You might even find you get better service from the crew (which might be useful if you're travelling with kids) due to the smaller cabin.

I'd hope anyone would try to have a little consideration for people around them, and would pick seats accordingly (parent or not) - the fact that the OP bothered to ask suggests they probably fall into this category. Many don't, sadly, but I suspect they're not going to come on here asking advice.