What a horrible tragedy for this family.
Everyone wants to find someone to blame, because they want some assurance that this couldn't happen to THEM. So they blame the parents, or they blame Disney. But the reality is that playing on the beach, even at the edge of the water, is not really dangerous in any objective sense. The evidence (albeit non-scientific) is in this very thread. How many people have posted that their own kids have waded in the water? How many have posted that they've seen others do it? How many spend time on the beaches or using small watercraft on the lake itself every single day? And out of all that, how many have DIED from an alligator attack, or even been injured?
Was there a risk there? Sure. But every time I walk down the sidewalk, there's a risk that a car might jump the curb and run into me (or my kid). When I go out in winter, there's a risk I might slip on ice and crack my head. And let's not even get started on the risk I take with myself and my kids when I get in my car Every. Single. Day. Tragic things happen sometimes, and it's not always someone's fault.
Was it wise for a small child to be playing at the edge of the water, at night, in a season when alligators are known to be aggressive? No. Was the result foreseeable? Maybe, in the sense that something like this could probably be assumed to happen eventually. But there was no reason for either the parents OR Disney to assume that an attack was even remotely likely. If you put enough cars on the roads, it's inevitable that some of them will collide, and people will die. Does that mean we should all stop driving? Or, in this case, does it mean that Disney should put up fences, and nobody should ever be allowed to enjoy the beaches again? I don't think so. More specific signage might be reasonable, but some risk is inherent in life, no matter how many signs you put up.