Yes for heavens sake use headphones. On a recent flight back from SC two teenagers were watching a movie, no headphones at a loud leve. The movie had a substanital amount of profane language and such. I was very happy that my 6 year old son was not with me. A mother with young children politely asked them to turn the volume down and the father I beleive of the teenagers snapped at her. Needless to say, we all ended up listening to the vulgar movie for about an hour and a half.
On another note, we have brought a DVD player and Gameboy for our son on numerous flights. Probably will do so again in Sept even though our flight is relatively short. That way our son will have his headphones on and not have to listen to other people's garbage.