First, I did see your later post, so mine is specifically about your proposed NW route.
Even with a month, I don't know if you'll want to go all the way to Seattle with your kids. While Mt. Rainier is pretty cool, the return trip along US 101 doesn't have as much ocean scenery as one might expect. I go at least as far as Mt. St. Helens, as your kids will enjoy it and it's a learning experience to boot. I know Lassen NP isn't terribly far from where you live, but if you haven't been there, it's worth the small detour on the way up. There are volcanic hot springs and paint pots there. May not be Yellowstone, but the kids will at least get the idea.
On the way north, there's Lava Beds NM (miles of lava tubes to explore, great fun for kids), Crater Lake, lots of activities around Bend (stop at the Lava Lands Visitors Center for info), hiking to waterfalls in the Columbia River Gorge. We've spent a week just in the Bend area there's so much to see and do. Never rafted there, but have heard the Deschutes can be quite fun.
Coming back along the OR coast, one can easily spend a month and feel rushed with all there is to see and do. Don't miss the Tillimook Cheese Factory. Amazing selection of ice cream.
I've posted itineraries with lots of links in the past. Rather than try to recreate them, please check out:
post 1Post 2If you feel a need to go as far north as Seattle, maybe you might consider camping at Deception Island SP and taking a day ferry trip to one of the San Juan Islands. But personally, I'd stop at Mt. St. Helens and start back. The kids will have more fun outside exploring compared to being stuck in the back of a vehicle for an extra couple of days.
As far as reservations, you are going to some of the most popular summer destinations where CG's fill every day during the summer. I've always found the best campgrounds are the ones that fill early and they're full for that reason -- they're the best. The OR coast is particularly popular. We've camped along there on several different summer trips, and the CG's were always completely full. I'd rather have a reservation so the kids can walk from the campsite to the beach rather than being a few miles away and having to drive them there. But as someone said, "Your mileage may vary".
