This question was answered on our Q & A Wednesday show on June 14, 2017.
Children do not generally receive special pricing when booking a cruise. If they occupy a third or fourth berth, there may be a reduction the pricing, but that is not age specific. Occasionally cruise lines do offer Kids Sail Free promotions and this can really help families trying to book a cruise. MSC Cruises is the only cruise line to offer a regular Kids Sail Free program, where kids 11 and under are free on many sailings when two full-fare guests are booked into the same stateroom. Disney Cruise Line also offers regular discounts applicable to children based on their age.