I totally agree with jack2007 on this. They should limit the age to at least 3 years old.
Babies at that age are still trying to acquire immune responses to their normal environment. Put them in an environment with external germs and viruses from all over the world, of course there are going to be possible problems.
Another reason is that the ship's medical staff are not Pediatricians that specialize in infant care. I think they did the right thing.