^ It has been happening since day ONE.
(Info from Wikipedia, but I think I wrote this paragraph, and I am editing it a bit)
On Monday, July 18, 1955 crowds started to gather in line as early as 2 a.m., and the first person to buy a ticket and enter the park was David MacPherson (A young Adult in College). Walt Disney decided to have a photo taken with two children, Michael Schwartner and Christine Vess instead, and the photo of the three always carries a caption along the lines of "Walt Disney with the first two guests of Disneyland." MacPherson, Schwartner and Vess all received lifetime passes to every single Disney-owned park in the world.