Roadtrip from Portland, OR to Redwoods in CA

Is this a round-trip? And much time will you take?

Yes, round trip. Probably a week.

That;s fairly speedy ... you could limit yourself to Jedediah Smith Redwoods State Park, at Crescent City ... its Stout Grove is excellent, and very family-friendly. I think it's superior to Redwoods NP. Although Prairie Creek Redwoods State Park was good too, and it's just north of Redwoods NP (which is a peculiar mix of jurisdictions).

Also in Crescent City there is the Curly Redwood Lodge, whose one claim to fame is that the entire place was made from the timber from just one big tree. Sadly, this isn't enough to recommend it.

At Klamath there is the Tree of Mystery, which is a large souvenir shop with an excellent Native American museum tucked in behind it. Recommended.

I'm not a big fan of the Oregon Coast ... I just don't get the attraction. So given your short time, I would just use the Interstate to go south to California. On your return trip I would recommend heading via Crater Lake NP, Bend, and Mt Hood. But time is your enemy.

Is this all motels? Any camping?

2 Nights - Oregon Dunes National Recreation Area, it's a fun place, maybe rent some dual ATV's with the kids or just hike some dunes.
1 N - Crescent City for Jedediah Smith Redwood State Park, hike Stout Grove, awesome hike and easy for the kids. Enter from the SP and over the river on the walk bridge.
The coast drive is awesome!
2 N - Humboldt Redwoods SP, stay in/by Avenue of the Giants, great park and lots of short hikes. On the way down maybe stop for a couple hours at Trees of Mystery, looks cheesy but folks here really like the Indian Museum and I think the kids would like it overall. Might be an Elk Herd around Orick, keep an eye out.
FYI, Redwoods NP is very average at best, easy drive through.
1 N - Redding via Grizzly Creek Redwoods SP, maybe go for some wading in the river/creek. Hwy.36, it's very slow and curvy but very scenic to Hwy.3, up to Hwy.299 and over to Redding.
1 N - Chemult via several hours checking out Crater Lake, old style town, lots of outdoor activities and easy hikes.

Back to Portland via Mt. Hood, nice drive.

Be easy to cut over after Jedediah Smith over to Crater Lake if you want to drive fewer miles but Humboldt is very cool and well worth it.
https://goo.gl/maps/s8Ndn4hBVeG2

My grandkids like Lassen Park

It is a little off the road, but the kids would love Oregon Caves National Monument. I must admit I am partial because I was a cave guide there 52 years ago.

My standard Trees of Mystery post:

Trees of Mystery at Klamath, CA, between Eureka and Crescent City, You can't miss it. It looks like the world's most godawful tourist trap with huge statues of Paul Bunyan and Babe the Blue Ox in the parking lot. Ignore the Trees of Mystery part and head for the gift shop. March past the tacky souvenirs and in the back you will find one of the finest American Indian museums anywhere. Local Indians first told me that it was a must visit. The Trees of Mystery stuff supports the museum which is free.

I'd like to clarify something that might cause you a bit of confusion if you are searching for information about the California redwood parks . What is there is called Redwood National and State Parks. It is a collection of four parks that are managed as a single unit. Jedediah Smith, Del Norte Coast, and Prairie Creek are state parks. The rest is National Park.

We're looking for an itinerary (including towns to overnight in) for a 4-day round trip Portland - Redwoods for a family of 3 (including a 17 year old). We like 3-4 hrs driving every day plus time for outdoors (hiking, beaches etc.). Ideas? Trip plans?

@srivanijade916908 You will get the best answers if you start a new thread, rather than replying to a very old one. More people will see your post.

When you make your new post, it will help if you include the dates you plan to travel, your approximate budget per night for lodging, if you are interested in camping, and what you like to do besides outdoorsy things.