Boy Drowns in Cinderella's Moat: On August 11, 1977, a 4-year-old boy from Illinois drowned in the moat surrounding Cinderella's Castle after he wandered away while the family was waiting to watch a parade. The family sued Disney for $4 million and, after nearly nine years and multiple trials, won the suit. But the award was reduced to $1.5 million after the boy’s mother was found to share the burden of negligence with the park, which didn't have adequate fencing up around the moat.
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.