Based on the rules of all cruise lines, not just Carnival, the cost for a child under 2 years old, on a Carnival cruise, is the same price as any age of a child, because they don't charge by the age, they charge by how many guests are in the room. They do, however, give discounts for the 3rd person in a room. We found this out when we paid for my granddaughter to go on a cruise with us, last year. You also have tips that you have to pay for the 2 year old, as well. The price varies, depending on which ship you go on, how many days the cruise will be, and which type of stateroom you want.