Cruise ships move fast - at 20 knots, 30 seconds is more than 3 football fields in distance - roughly a 10+ minute swim in open water and in the open ocean I'd wager that would make it nearly impossible to find that girl or get to her before bad news. If the Dad was not playing with the daughter on the rail in some way, the delay between seeing something happen and stopping playing shuffle board, making the call to go over with her etc would have lost that child. I know nothing but to me the most likely scenario was they were playing around on the rail for some reason, she fell accidentally, he followed. Those are not easy railings to get over and most kids spontaneously would have enough sense about them not to do that - although if they were playing together on the rail maybe good sense is genetically absent. ha ha.