Hyperion Theater Death: On April 22, 2003, a stage technician fell 60 feet from a catwalk in the Hyperion Theater at Disney's California Adventure, prompting an investigation and fine by the California Occupational Safety and Health Administration (Cal/OSHA). The victim did not regain consciousness following the incident and died a month later.
Seriously though I am surprised deaths don't happen more often. The Walt Disney parks had 132,549,000 visitors just in 2013. So just in that year alone the average was more than 37 thousand people per day.
I'll bet you it is statistically safer to play and have fun inside their parks than the trip flying or driving there.