I'm the family cruise editor here. I recently wrote an article posted on this family section of CruiseMates.com which tells about the youth facilities on new ships. There is a section on the Navigator which has great kids' and especially teens' facilities.
Last year my eight year old cruised with us on the Adventure of the Seas and had a fabulous time -- it was her 12th cruise so she's a good judge of fun youth programs! Royal Caribbean has a high action youth program which I rate very high.
Smooth sailing,
Luisa Frey Gaynor