No one knows if this guy was even a good swimmer. Not everyone just floats when they get in water.
I think I would have gone onto my back in the water and laid the child length wise across my abdomen while holding it with my left arm, and swimming with my right arm and legs to shore, or wherever I could get to quickly.
At least on your back you can always breathe, and the air in your chest will help you remain afloat.
Dunno if that would have worked, but that would have been my plan.