First off, I can't imagine anything less relevant to the story than how deep the water was. The child was two years old. That puts him at about 34 inches of height. If he had been in a foot of water, the water would have come up past his knees. I am 6 feet tall, and a foot of water would come up to my mid-calf. I certainly don't get the impression that the father was in calf deep in the water or that the child was up to his thighs. The more likely scenario is that he and his dad were walking on the sand in the area right where it meets the water. Two to three inches, tops. But that is plenty close to catch the attention of an alligator. And it really doesn't matter.
Signs. Walls. Fences. People want to find blame and assume that proper measures weren't taken. But as pointed out, this is the first alligator-related fatality since 1971, and only the second known alligator attack in 45 years. It is irrational to think that a company is going to take extraordinary measures to prevent such a rarity. Think about how many people have died or been seriously injured at WDW since 1971, and now compare that to alligator attacks. Disney has plenty on its plate before it needs to account for the once-every-45-years accident. And that is what this was. No one is to blame. The humans were doing what humans do. The alligator was doing what alligators do. When the two intersected, a tragedy occurred. By all accounts, Disney already searches for and removes alligators that it believes might pose a threat. That is a sensible reaction, and they already do that. But they weren't perfect, obviously. And a family lost a precious boy in part because Disney wasn't perfect, and in part because the family went into water that they weren't supposed to be in, three inches, a foot, or otherwise. When people and/or corporations fail in their quest for perfection, then things like this happen. But are we really at a point where we expect either the parents, the child, or Disney to be perfect? Is the lack of perfection blameworthy?