Had a screaming child ~2 years old two rows ahead of me in J on Air Canada two days ago. Mother walked him in the aisle a few times which did quiet him down, but as soon as he was back in the seat, he yelled and climbed on the side table area. The the flight attendant firmly forbade that, but he kept trying to get up over the seat to the one behind. Mom basically let him do whatever; Dad in the next seat (we were in the middle row) ignored it all. I walked past on the way to the washroom and saw he had no toys, only the amenity kit to play with. When I travelled with my children, my carry-on was stuffed with surprises to keep them occupied. I reflected that back in those days the airlines gave children little goody bags. They went some way to keep children whose parents hadn't thought to bring toys quietly busy.

I wore Bose noise-cancelling headphones, which helped a lot with the plane noise but were no match for the high-pitched screaming.

I have travelled a good bit in all classes, and disagree with those who say a loud drunken adult is worse than a screaming baby. I've never run into such a disruptive adult passenger but have had my share of flights ruined by the children of heedless parents who care nothing for their fellow travelers. But why would they, they don't even seem to care about their crying children.