I am been thinking about this. As a dad of a toddler, I have to think that dad did everything he could think of in that instant, and is now blaming himself for not doing more. That said I don't know that more could be done. If the gator gets it's jaws locked on and is in the water not many humans would have much ability to do anything other than maybe being able to hold the gator up and waiting for more help. But even that would be extremely difficult.
As suspected if this was a 4 foot gator, dad wins. Going to guess it was considerably bigger than that, this is from the article below.
"Of the more than 750 alligator complaints investigated by the DNR each season, more than half involve small alligators less than 5 feet in length, according to Rhodes. Alligators of this size feed on crawfish, aquatic insects, small snakes, frogs and turtles. The average body weight of alligators 3 feet in length is not quite 4 pounds. Four-foot alligators average about 11 pounds, while gators measuring 5 feet average only about 22 pounds. Children and dogs that exceed these body weights by a factor of several times are not in danger."
http://www.southeasternoutdoors.com/wildlife/reptiles/article/small-alligators-not-problem.html