However, it is highly probable that Disney will be found to be negligent. Negligence occurs when a party does not prevent or properly warn of dangers that are "reasonably foreseeable." Given the well-known existence and prevalence of alligators to people native to Florida, Disney was certainly aware of the alligator threat. In fact, the have a special team of people dedicated to removing dangerous animals (per the press conference). In spite of that, Disney creates a zero entry beach, sets up lounge chairs, and hosts movie nights near the water's edge. All of these things signal to the average visitor that the beach is a safe place; it even makes the water inviting! Aside from a "No Swimming" sign, which has been shown in this thread can mean different things to different people, Disney has apparently not warned guests of the threat. On top of that, there have been numerous reports of people watching kids splashing or wading the in the water. It seems that Disney never asked the kids to stop splashing in the water; once again, it gives the impression that wading in the water is safe. My opinion only. However, according to the press conference, there is an active investigation.
There is NO question that Disney will be on the hook for negligence for the reasons you described. They know it (at least their lawyers do) and they do not want the publicity of litigating against this family. Therefore, not that it is ANY consolation, but Disney will be settling this with a relatively enormous sum of money.