My son (5 years old) did not do it on the Fantasy but we did do it on the Dream a few weeks ago. While I did think it was cute and a good "one time" experience, I would not do it again.
Here is a brief description of the tea party. Bare with me because I am really bad a describing things.
First, each little prince or princess is announced by Lady Chamomile - Prince or Princess "so & so" of the Disney Dream. Lady Chamomile is the lady holding the tea. Then each little princess is crowned with a tiara and each prince gets knighted and handed a sword.
You are then escorted to your table that is set up with all the tea trimmings. All of the girls had a Cinderella doll waiting for them in their chairs and a jewelry box with a bracelet sitting on their plates and autograph books and pens sitting next to them. The boys had a shield in their chairs, a Duffy Bear dressed like a sea captain with a bag to carry him in, and an autograph book with pen.
Lady Chamomile and Chef Brule sing and do a little skits and announce a special princess guest. After each princess was announced that princess would walk around to each table and greet the children. They would sign the autograph books and take pictures with the kids. Footmen would pass out special gifts to each of the children that the princesses would bring them. The girls got a charm for her bracelet and the boys got a trading pin. The princess that were there were Belle, Snow White, & Cinderella. At the end of the tea party every child got a picture with all three princess together and before the cruise was over it was delivered to your stateroom in a frame. There was a lot of interaction with each princess.
Lady Chamomile and Chef Brule were hilarious and even the adults were laughing.
I hope all of this made sense!