hjello, all the posts above have pretty much the same advice and all of it is very good advice. Your 8 month old will be too young to have any memories of cruising or appreciate the experience the way Mom & Dad will. Bob mentioned that Grandma would be a great choice to care for a baby while you enjoy each other and some alone time. Lugging a baby on the ship, to dinner, excursions, etc. can be a real challenge. Not to mention missing some of the entertainment and port things because of feeding times, nap times and general times of the child developing a less tollerable dispositon after all the loud noises, long days, hot sun and other factors that will be a drain on all involved.
Daves advice of 2 years and above lets them at least be old enough to know what all the stir is around them and enjoy the attention that will be lavished on them by other passengers.