Cruise lines that offer "kids sail free" promotions vary each year depending on the cruise market. However, on MSC Cruises, kids 11 and younger always sail for free. Other cruise lines that sporadically offer "kids sail free" promotions include Crystal Cruises, Disney Cruise Line, Royal Caribbean and Norwegian Cruise Line.
MSC Cruises, an Italian-inspired small cruise company, is the only cruise line where kids ages 11 and under always sail for free, as of 2015. Kids ages 12 to 17 can sail for a reduced rate. This deal applies only when children are booked as the third and fourth guests in the same stateroom as two paying adults.
Other cruise lines generally offer limited "kids sail free" deals or accommodate children at deeply reduced rates when they are having trouble filling up their ships on upcoming voyages. Savvy travelers should look out for these promotions about 45 to 90 days from a particular sailing. Crystal Cruises offers "kids sail free" on select voyages throughout the year, where any third guest under the age of 17 can sail for free. Disney Cruise Lines, Royal Caribbean, Norwegian and other cruise lines don't offer the promotion often, generally once or twice a year.
Most "kids sail free" promotions are for a very limited time and go quickly, so travelers should book as soon as possible. Keep in mind that taxes, fees and gratuities for all passengers still apply, so no "kids sail free" promotion is truly free.