Sea Lion Caves are a ways South of where you're ending up, those are close to Florence. If you want to see a dozen sea lions or seals or whatever instead of hundreds in a cave that smells like guano, there's a little "feed the animals" aquarium in one of the coastal towns closer to where you'll be, I can't recall for certain if that one's in Seaside. There's a real aquarium (The OSU/Hatfield facility) in Newport where kids would get to check out/touch octopi and star fish, but rocky tidal pools elsewhere all along the coast will offer much of the same thing. Get a tide table and figure out when is best to check out rocky areas for star fish/octopi and looking for agates and sand dollars on beaches.
If you go South, between Florence and Coos Bay is the Oregon Dunes National Recreational Area. If you own a dune buggy, you'll wish you brought it along. There may still be some good fresh water pan fish in the inland lakes nearby.
Everybody stops for ice cream in Tillamook. I think it's required.
On Hwy 101 along the coast, be ready for bicycles and RVs slowing up traffic. Bring binoculars for when you stop to park. Like when overlooking the ocean at Oswald West State Park. Be a tourist and check out Haystack Rock by Cannon Beach and get your picture taken.
There are DOZENS of drop dead gorgeous places along the way. Lots of tide pools. Miles of wonderful beaches. Lots of COLD salt water, featuring crazy kids turning blue, golden retrievers eating whatever is washed up, and a few adults in partial wetsuits playing with short boards. If you have a water dog along, it will throw up from too much fun at some point.
Don't take little kids along if you want to hike up Saddle Mountain, inland from Cannon Beach. It's a 3,000 foot elevation gain and it's too much work carrying kids when they go on strike half way up.
The trees have grown a lot along the coast near Fort Stevens, close to Astoria/Warrenton, site of a Jap sub shelling the coast during WWII. You can walk around bunkers and artillery exhibits but you can't imagine spotting the sub yourself from the observation posts because those trees now block the ocean view. Part of an old shipwreck (the Peter Iredale?) is still accessible on the beach near by.
Maybe the casino in Lincoln City has roulette, so lock up your money in your car.
If you are meeting someone who owns a boat, there are bunches of good places to go crabbing, but I'm not in tune about good/bad seasons for best results. There are lots of charter fishing boats out of Newport and probably also Tillamook and Garibaldi and other towns along the way. Lots of good chowder. And you can lose many brain cells at brewpubs in Newport (Rogue Brewing) and probably Cannon Beach too.
You want forests? There are some "valley of the gods" virgin forest old growth stands down in Lincoln County, inland from Newport or Lincoln City. Twisty roads? You may have to get off US 101 and check out Hwy 6 along the Wilson River. You will see traffic but also a tree or two along the Van Duzer Corridor on Hwy 18. When I moved here from the Midwest, I got a sore neck there checking out the trees.
Some places to stay on the bluffs above the beach have hot tubs, and that's a horrible way to spend the evening after too much driving or getting sand in your shoes or chilling your calves in ocean water.
