If I could trust the airlines not to lose my bags, not to make me wait in a 2nd line to put my checked luggage thru the screening bin, not to break things and not to make me wait up to 45 minutes to pick up my luggage then I might check more things. However they don't do this so I will carry on if possible.

On topic regarding the falling item, I prefer aisles as well. I always watch above me when someone opens the overhead for two reasons: 1. that no one is taking my belongings and 2. so that I don't get beaned like the poor kid.

I learned the watch for falling objects after a flight I took where a lady (and I use the term loosely) that was two rows behind me but had had stored her camcorder above my aisle seat tried to reach across two rows upon landing to retrieve her camcorder. Well she grabbed the shoulder strap and pulled on it and of course it came swinging down and nailed me right in the shoulder then fell in my lap and then to the floor in front of me when she let go. Don't ask me why she let go, I don't know. It was in a padded case and it hit me in the shoulder so it didnt do any damage but it hurt like you read about. I will tell ya this though besides learning to watch for falling objects, I gave the camera a nice swift kick into the space under the seat in front of me and the person an earful. To this day I don't know why she couldn't wait till she passed the o/h bin to retrieve her item. Had she waited, this would have never happened and her camera might have made it to her destination without the results of a nice swift kick.

Based on this experience I've learned not to let any child (at least small child) I ever travel with sit in an aisle seat.

As for liability to your son's injuries, I would think someone is at fault but even after reading all of this, I can't figure out who.