I was on the Navigator of the Seas in August 2004. The Mariner is the newest Voyager class ship and the Navigator is the next newest.
Most of the kid fun things are in the back upper decks. There is an in line skate track, a mini golf course, a basketball court, a rock climbing wall, several table tennis games, a video arcade. There is a special area just for teenagers. I don't remember if it is for 12-18 or 13-18. I understand the counselors will kick you out if you are over 18. I peeked in early in the morning before it was offically open. Looks pretty cool. There is an area to just hang out, several computer stations, a dance floor, a soft drink bar, and a DJ booth. Right next door is Johnny Rockets. There is also a large rear deck area reserved for the kids. I am sure he will have a great time.
I am from California, but I will not be crusing out of Florida this year (leaving out of Long Beach in October and then the Eastern Caribbean in April of next year).
I hope to be able to cruise on the Mariner or maybe the Freedom in 2007 or 2008.
Have fun! :-)