Costa, the Carnival Corp. subsidiary known for affordable Europe cruises, also operates in the Caribbean during the winter, and this year it will let children sail for free on 12 Caribbean departures of the Costa Fortuna—including its Christmas and New Year’s cruises. The ship sails out of Ft. Lauderdale on alternating seven-day eastern and western Caribbean routings each Sunday, from December 21 through March 8. Fares for parents start at $669 per person, and the offer is good for up to two children age 2-17 sharing a cabin with two adults. (For people without kids, the fares for those sailings currently start as low as $499 per person.)