I understand where you're coming from and had a similar experience on a flight to Hawaii some years ago, where a nearby child in the lap of his mother screamed for a solid 8 hours. It was agony.

My understanding of the problem is that children don't have the ability to relieve the pressure in their ears, so the plane flight is physically painful for them. There's no way to explain to the child how to "yawn to let your ears pop" when the child isn't able to speak yet. And there's no good alternative transportation for getting to Hawaii. And unfortunately the pressure inside the cabin of a high-flying aircraft varies.

Having experienced this myself, I don't think "headphones" are the answer. (You'd need either sound canceling or sound reduction headphones for them to really help, which would require planning for this issue in advance.) Earplugs help /some/ but even with them the sound is amazingly annoying.

After the flight was over, as a joke we came up with the idea of marketing a can of nitrous oxide (laughing gas) with a baby nipple on the front of the nozzle with the label "Scream Away". Probably wouldn't help if tried literally, but the thought was worth a laugh. Later we played with the idea a bit further and came up with the idea that pirates could use cans of "Scream Away" when marauding nearby ships. :-P