I have to disagree about a one month old going nowhere unless someone dropped him in the water. A number of things can happen especially on the tender. The tender could hit something in the water. The tender could be hit by another boat. The motor could jam and stop suddenly. The law requires that people wear seat belts in a car. It's no different for a baby on a boat the size of a car.
As for the yacht, when under sail, as we've seen, it can heel significantly or have a sudden wind shift. We've seen people lose their grip and start to slide. If you're on the deck, that could possibly put someone in a position of losing their grip of the infant. That child could possibly go overboard. I would never take a chance like that.