Screaming kids are easy to ignore on most flights but I recently had one on a 14.5+ hour flight (Asia to US). Screamed 10-20 mins every 1 to 2 hours. I got 2 hours of sleep and felt as if I had the flu.
I find that noise cancelling headphones make everything quieter, and then cancel out all the low frequencies... Leaving nothing BUT crying for you to listen to!