Actually, drowning is a leading cause of death among children. It is the #1 cause of accidental death for kids ages 1 - 4, and the #2 cause of accidental death for kids ages 1 - 14 (right behind car crashes). I've personally seen multiple children in real distress in the water be rescued by lifeguards before.
So there is nothing unusual or unlikely about children drowning. That happens regularly, unfortunately. Unlike a real cruise ship emergency, which is very unusual & unlikely.
I never said to not have muster at all. I described a modified muster that would allow people to not be squashed together in a tight group for 20 minutes at a time. People would watch an instructional video independently, put on their life jackets (a part of the traditional muster drill that is currently neglected), and go to their muster location on their own schedule.