I've never seen anything which I would consider disturbing on the main screen. For the multi channel screen I wouldn't allow my kids to watch anything I considered violent, but to shield them completely is unrealistic. I'm not concerned about a sex scene in a film but I draw the line when sex is mixed with violence, though I doubt you'd ever see that on a plane.
Avman is right about the violence in childrens film material, especially some of the older cartoons.
Most movies will have little effect on kids but some will, I recently caught my nine year old watching the 'Blair Witch Project' which he'd taken from my DVD collection, that movie scared the sh*t out of me so I'm glad I caught him whilst he was watching the starting credits.....