I consulted with my twin's pediatrician prior to taking them on their first cruise at 9 months old and he didn't have any problem with it. As he pointed out, they are exposed to germs everyday in places like the shopping mall and grocery store. A cruise is no different. The only way to keep them safe from germs is to lock them in the house and never let them out. Which, by the way, he said would be one of the worse things you can do for their immune systems since if they are never exposed to germs they will never develop immunity. Of course, every child's health situation is different, so parents should definitely consult with their own pediatrician prior to planning a trip.