PK,
Getting detailed to San Diego for six months I found it at first to be one of the most boring cities around, well when you are spoiled rotten on 24 hour a day living in Chicago, San Diego is one of those towns that rolls up the sidewalks at 9 pm.
But I would check out the San Diego Wild Animal Park, that is good for a day, not to mention the regular San Diego Zoo, zzgundamnzz is right on the money with wandering around Coronado, especially the beach, if the kids are lucky, they might catch the next SEAL BUD's class hard at work, or see them boucing around the Coronado Bay in their Go Fast boats.
I'd let them wander around La Jolla, some really decent shopping there, and a lot of little hotties spending daddy's money or doing some quality window shopping.
Del Mar for the surfing, and up the road in Cardiff by the Sea is one of the best health food resturants on the west coast, its called Ki's Juice Bar and the clientle there is extremely easy on the eyes.
Further up the road is Legoland California, and before you re-remind me that they are 16-17 year olds, you are never too old to mess around with Legos.
Hope this helps!