We recently flew on UA from KOA to LAX. We were in first and my 14 year old son was in coach on an aisle. We deliberately put him in the aisle so he could get in and out without bothering anyone. When I looked back there was a man in the aisle, a woman with a lap baby in the middle and my son in the window. I went back and told them that I put my son in the aisle so he could easily get in and out. The man replied, "Well we need to be able to get in and out because of the baby." I replied, " That is my son's seat." My son said he didn't mind so I left it alone. Later, I noticed my son was in the aisle. I don't know if they moved because of me or if they realized it was not their seat.