I believe the signs only said no swimming. I think this being at Disneyworld, they should not have sugar coated it and plainly stated on the sign that there were possible alligators. There are so many signs at amusement parks that say do not enter and no touching, the parents probably thought nothing of it at the time.
Knowing how many children from all over the world attend this park, who speak different languages, disney probably should have had an image of an alligator on that sign (kids can't read also), if they were not willing to completley purge the area from the monsters and fence it off anyway.
We all know that disney can afford safety. After all, it should have come first anyway, and its a childrens park for crying out loud...
Just my 2 cents.