I remember a flight from Paris to JFK with a small child kicking the back of my seat all the way.
All children under the age of 16 should fly as checked baggage.
In case it's cold and/or depressurized, they can have a wetsuit and SCUBA gear, and they'll think it's a game.
On a flight years ago I had an aisle seat in the center section. The other four seats had a couple and two small children. I had had a bad week on the road and just after convincing myself it would be a miserable flight the father handed me a couple coupons for a free drink. As it turned out the kids were well-behaved and I arrived home in a good mood. :-)