We have a 14 year old daughter and 10 year old son. Before we purchased our boat this past year, they had some experience as we day chartered about once a year. In the past few years, my kids have been mostly passengers on Lake Michigan, the Chesapeake, and the Nile (on a captained faluka [sp?]). These trips were very good experiences for us all, despite a short and severe summer storm in the Chesapeake. They both now enjoy sailing, but the real benefit for us is that it is a family activity that we all can enjoy.
My daughter must be a typical teen: always gives me grief about going, but has a good time once she gets there. Our first trip was particularly difficult, the two of us sailed from the C&D to Atlantic City; My wife basically guilted her into the trip. Once she got over the fear, she enjoyed the independence and control. She even took up windsurfing at summer camp and when the homework load is too heavy, she brings it with her. Despite the resistance I get, she is a real joy once we get on board.
My 10 year old boy is real joy: he'll come with me anytime, and is wiling to work, in fact, he even looks for tasks once we're there. If he brings a friend, they both become very distracted and usually wind up chasing crabs on the dock. (They're great underway and when they have a specific task to accomplish... however, I am not a micro manager.) If I have a specific task to perform, we dont bring friends. His primary condition for a two month cruise is making sure xbox-live works on board. (I havent checked the bandwidth requirements yet.)
The primary issue appeared to be fear.. this issue is being overcome with knowledge and experience. She said, "I'm not really sure why I was so afraid." The other thing I find that works is keeping them involved and giving them responsibility while avoiding too many "chores." Another issue is that my daughter gets anxious if she cannot check in daily with her friends on facebook and the like. I usually bring some sort of Internet device just in case i need to fix something at work. (Mr Murphy knows when I am off the net.) I let her use it at night.
Next season we're looking for a dock/mooring that is closer to a social scene. I expect this will provide some training for the kids and perhaps a more social draw for them.