Hi there, we sailed on the Zaandam in April 2011, along the Mexican Riviera, sailing from San Diego. Our 13 year old daughter was one of the 21 kids on a ship with about 1500 passengers. The kids ranged from babies to just a couple of teenagers. We found that there were not much to do for kids. Whilst there are children's clubs, each time my daughter went along, she found the room empty!
Not sure if its the itinenary, but we found the cruise to consist of at least 80% of passengers over 60 - with many over 80 years old. The shows and entertainment (quizzes) were geared likewise for the older passengers. Typical daily quiz will be based on 1950's events or 1950's music and songs in the shows from the 1930's.
Although we enjoyed the cruise, the staff and service are excellent, we found that it is not really geared for children or family with children. Our daughter just spent the sea days with us by the pool or watching a movie in the cinema.