As little as possible! They cost enough when they get older!
There is no standard rate to cover all cruise lines. On some, kids go free all year/parts of the year. Some have a 3rd & 4th person rate irrespective of age. Some have a child rate which varies with age & cruise line.
Im resisting the temptation to make a joke about this question.
Oh go on Roberts or I shall have to do it for you!!!!Here goes then-----" I don't know, I've never bought one"!!!Sorry . Cynthia.
I bet you couldnt eat a whole one lol.