Contrary to most things I read before taking my 9 month old on his first airplace trip, it wasn't his ears we had trouble with, but his bowels! He had such a massive BM, the flight attendants were handing us trash bags as I changed him on the floor of the bathroom (only one plane that I have ever been on has had a changing table). He also had a repeat performance on the return flight.
DS was 10 months old, however, on his first trip to WDW. He, too, had a wonderful time. He didn't enjoy the shows too much, but he loved the 360 degree movies and anything that moved. He slept alot at the parks, but that's when we would do "switching off". Actually, I believe the way it works is that if you are switching off, your 5 year old (if up to it) would be able to ride with both parents.