Yes, its pretty pricey to bbuy passports for everyone, but now you have the ability to travel international with the family without having to worry about it. Also if something unfortunate happens while you are on your cruise and need to fly home, you can do so without worry. Its expensive but the piece of mind is a good thing.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013