I just got off the Triumph last month, I had my 16 year old son with me. I have remarried and have a different last name than him. They never questioned anything about it. She did look at his birth certificate and then at mine and I guess that since she saw that my first and middle names were the same on both documents that it was me. I had a notorized letter with me tho just in case. It simply stated that I had his dads permission to take him on the Triumph on the November 10th sailing.
I have also taken my stepsons on cruises and have never been questioned about it. have a great cruise.