One of my colleagues ruptured her eardrum from flying during an ear infection. She had to be carried off the plane because she temporarily lost her sense of balance (on top of terrible pain before it burst, and temporary loss of hearing). Once the eardrum bursts, the pain stops, but why do that to a kid? A burst eardrum will heal, but scarring from it might mess with your hearing for life.
The duration of the flight is irrelevant, it's the pressure increase during landing that matters.