We did a family cruise to Alaska last year when our son was 14. He seemed to enjoy it, particularly the calving of the glaciers. I'd suggest an Inside Passage cruise because the open jaw airfare can be expensive for a family.
Bermuda is a great family destination, as well. There are many beaches, a wonderful aquarium, and forts to explore. Best yet, the public transportation system is wonderful -- easy to use, and easy on the wallet. It's also nice as the ship stays docked for a few nights, so you won't have to rush back each day.
Just a couple of ideas...