Ok, I stayed out of this thread for a long time, but since it refuses to die, I'll chime in.

From about second grade on, there is no excuse for poor behavior. 7 year olds go to school, and presumably have learned how to behave in a community in a quiet setting. I believe that it is the parent(s)' responsibility to ensure that their child behaves, and take appropriate actions if this does not occur. As my cousins (8 kids between 3 of them) say "I'm the mom, you're the kid."

But, very rarely do I see a 7-11 year old misbehave on an airplane. They're usually great, and it's harder to be an accidental seat-kicker with 40 inches of pitch... When they are not great, their parents are often not model passengers, either.

Younger than that, it depends on the child and the flight. But, I think the fancy restaurant analogy applies. Parents should use their judgement. We should respect parents that are obviously trying, and endure parents that are NOT trying.

But, I'd contend that my heavy snoring in transatlantic business class is just as annoying to a light sleeper as a slightly fussy 9-month-old would be....