I'm going a bit off-topic on the swimming pool question for a moment... Before taking baby on a cruise, be absolutely certain to get medical clearance fron his/her pediatrician. We've all heard the stories of norovirus, but while that is rare, it is far more common to pick up colds or sore throats, no matter where or how you travel. And, make sure that you get travel insurance that covers all of you if you have to cancel if you child does not get the medical OK to travel.
HAL has a wide variety of ships and itineraries. Which ones are you considering?