A couple other suggestions from someone who lives IN Seattle... :)
The Ride The Ducks tour... It's a tour of Seattle, on land and water. You're in an amphibious "boat" that also travels on land.
The Underground is an awesome thing, you'll both love it.
Seattle also offers a "coupon book" that gets you free admission into several "touristy" places, zoo, aquarium, Pacific Science Ctr, Museum of Flight and a couple others... Don't know if yours is a bit old...(your ds

)
The Southcenter Mall is having a renovation that should be complete when you come, they are building an add on, that they claim will be great for the whole family. It has a children's play center, and "something your teenager will want to 'get lost' in"
As far as eating...
Breakfast:
Beth's Cafe
Awesome food and entertainment...Plus, if you request the balcony, outside eating... When I was a kid, my step-dad was the Janitor AND a weekly musician (Lonnie Williams) at the Pink Door (so I was there all the time! :) Can't visit Seattle w/o going there!! (under 21 welcome outside bar too!)
Best BBQ joints:
Jones BBQ and OK Corrall
Great walking/parks: Greenlake (of course) and Discovery Park (beautiful in Summer!)
Another thing you should check out is the farmer's markets, not just Pike Place... you can google seattle farmer's markets for the times/days... They've got wonderful local produce, flowers, smoked salmon, jams/jellies/nuts etc. It's just great!!
Sounds a bit 'touristy' too, but you've gotta go to the top of the Space Needle. The view is amazing. I wouldn't necessarily suggest eating in the restaurant, only because it's expensive, but you can't beat the view.
Also, to check out what people who live in Seattle decided on as "best of" check out the best of
CitySearch website. (It's set on brunch, but you can check them all out...)
Oh!! If you have time, TILLICUM VILLAGE!!!!! On the waterfront in Seattle, they have trips all the time across the water to Tillicum Village. You go for a walk on the beach, have a authentic Native American meal w/entertainment, when I went as a kid, they fed local Salmon, and it was just the most awesome experience!! It's not too expensive, and I believe the meal is included in the price of the ticket.
HMMM...That's all I can think of right now, but I'm sure that I'll think of more... Just a thought, depending on when you're coming out
If you're interested in a Seattle Entertainment book, lmk.
HTH!!!