We've never been on a cruise before and thought the idea was a good one since Carnival featured several groups for kids. Mine are 14 (F) and 17 (M). If you've got teens, you know its a real challenge to keep them engaged and not "so bored they could die." Mission accomplished. Both kids had a blast. The 17 year old met with the "O2" (15-17 yr olds). They had their own club (supervised) and I barely saw my son after the first night. Carnival had scheduled events but also a lot of hang out time. My 14 yr old LOVED the Hollywood dance club. Almost every night Carnival had a dance for "Circle C" (12-14 yr olds), often w/a theme (big hair, 80's, etc). They also made T-shirts, played games, and more. We felt safe allowing the kids to roam around on their own.
As a family, we really liked that Carnival offered something to do almost around the clock. If you choose the Triumph, I recommend you don't miss the Showtimes (8:30 or 10:30pm)--a variety of Vegas style shows and comedy events. The dancers were true professionals. The Comedian Eddie Capone was funny and had a little give and take with audience members. The Magic Show with Kevin and Caruso was great too. ON the final night, your fellow cruisers perform--hilarious!
On the other hand you could choose to do nothing and just relax. Nice. FOOD: We ate at the South Beach Buffet on many occasions. Cafeteria style, good food. I recommend going to the dining rooms for dinner (either the London or Paris rooms). I wish I would've figured that out sooner. Crank up the ratings for food 10 times--from good to Outstanding! For first time cruisers: all of this is included in the price of the cruise package. ADVICE: get fit before you go. You can eat anytime, as much as you want, and may gain a few pounds (ice cream all day).