Attached is a form a customer service rep on the phone sent me. It was explained to me that you want there to be specific info about the ship and date of sailing as well as permission to make medical decisions. We've used it twice. Once they examined it and another time they never even asked for it. If you are uncomfortable with attachments I've cut and pasted it below as well.
Affidavit - Authorization for Minor to Travel
We, (First, Middle, Last Name) ________________________________ and __________________________________ hereby accept the conditions for my minor child