At TL we select a "Big Kahuna" who opens the park. Normally the greeters will chat with people on the lines before we open. About 15 minutes prior to opening one of the Lifeguards will come out and we may direct the lifeguard to a particular child or one is chosen at random. A bit of a fuss is made announcing the selection.
The Big Kahuna gets a medal on a ribbon, everyone in the family gets a special button and admission before anyone else. They get a free locker and first choice of where they want to set up, and other fun benefits.
Usually it is a child between five and ten years old. But they have to be there before we open the gates. This past year we had morning EMH seven days a week, so our selection really was limited to people staying at a Disney Resort.