Pre-paid, three words... Don't do it.
On the post about kids under 2 not requiring tips, not so. CCL's tipping guidelines are not age related. Just as you pay a fare for every passenger, every passenger pays gratuities. The ship sails on a head-count capacity basis. every child took the place of a possible adult in that capacity. The tipping guidelines are based on capacity not age. If you withold tips for children you'll have to visit the Purser and have them removed. This basically cheats crew members out of their expected income. If you like the crew to welcome children and provide exceptional service in the childrens facilities and programs don't withold their pay. That is what pays for the people staffing these programs and facilities.