My personal horror story occurred on the first three flights we were ever on with our daughter, who was an infant at the time. I don't know what her deal was, but on those first few flights she took, she'd have a mega blowout on the plane once we got up in the air. As luck would have it, all three times it happened, we were on planes without changing tables in the lavatories, so I had to improvise. Twice I ended up laying her on the floor of the galley (with the flight crew's permission, even though they weren't happy) to change her and once we changed her while we were sitting in our seats since we were experiencing turbulence and couldn't get out of our seats. That time, we were in a small regional jet with 2 seats on one side, so we didn't have a seatmate to annoy. And luckily, all three of these incidents happened when she was under 6 months old and still exclusively breast fed, so her excrement wasn't smelly (just very, very copious).
I have two horror stories that I've witnessed on a plane from other kids. They both happened when I was traveling alone on business on nonstop flights between MSP and SFO, so 4ish hours in the air, of course. One flight, a baby screamed the entire 4 hours. They were only a few rows away from me, so even blasting my iPod (which also isn't all that enjoyable), I could still hear the baby. I don't know how that kid didn't end up exhausting herself...she just would not stop. On another flight, I was seated behind the most rude, foul mouthed toddler I've ever encountered in my life. Demanding stuff from mom, telling her she was stupid, etc. And the poor lady just took it. That child berated his mother for 4 hours and she never once told him to stop. I was pretty flabbergasted.
As for the movie/iPad/small electronic device issue...I've never been so happy as when the FAA started allowing small devices to be on at all times. As soon as we're situated, we plug our kids in and happily let them rot their brains all the way to our destination. Anyone who judges us is dumb and the type of person who'd cut off their noses to spite their faces, IMO.
