Some suggestions based on the age of your kids (always my primary motivation when I answer).
Lava Beds NM in northern CA. Interesting CG. You can explore many of the lava tubes by yourself, no guide!. Take some headlamps and a backup flashlight. What boy doesn't like climbing around and exploring in a cave?
Link to info on lava cavesThen up to Crater Lake. Then on to Bend and the Lava Lands area.
Volcanic Vistas brochure another brochure For a different camping experience, check out some of the CG's in the bottom of Newberry Crater. Almost like camping on the shores of Crater Lake, as the sites are along the shore of the lakes at the bottom of the crater.
Near the Columbia River Gorge and Portland, we've stayed at Ainsworth SP. 40 FHU sites. But a big forest fire there a few months ago burned right near there. From what I can tell, the park escaped damage but many of the great trails to visit many of the falls were closed. You'll have to check when your departure date gets closer.
Mt. St. Helens is worth the drive off the Interstate.
Can't help you with Seattle as we try to avoid cities when we travel.
Near Port Angeles/Sequim, head up the Elwha River and hike an old road grade a couple of miles into Olympic Hot Springs. Take a couple of towels to dry off. Several natural ponds on the slopes across the river.
If everyone has a passport take the fast ferry from Port Angeles for a day at Victoria.
I am much less impressed with the highway along the WA coast compared to the OR coast. If time gets to be an issue, just head over to the coast from I-5 on US 30.
Along the coast, try visiting
some of the lighthouses. If the kids want to explore the tidepools, get
this brochure. So many places to see and stay along the coast. If you like cheese and/or ice cream, don't miss the Tillamook Cheese factory. Looking for a good seafood restaurant? Check out the Waterfront Depot in Florence. Reservations strongly recommended. Sea Lions at Depot Bay.
Sunset Bay SP has a really interesting beach setting. Beachside SP and Tillicum NFS CG are almost right on the beach. Harris Beach SP in southern OR is a good base if you're wanting to explore the redwoods of the northern CA coast. Cheaper than the CA SP's.
If you can fit in, Burlington CG at Humboldt Redwoods SP is a really interesting setting. Tough for long rigs as the interior roads are tight.
Ken & Allison
2 Camping Cats (1 diabetic)
1996 4Runner, TRD Supercharger, Edelbrock headers
2007 Fleetwood Arcadia, Honda EU2000i
4 mountain bikes, 1 canoe, 4 tents, 8 sleeping bags, 2 backpacks
(You get the idea!)