You’ll have a great time with kids in Southern Oregon! On the Oregon Coast, I highly recommend staying at Whaleshead Resort. They have very unique and beautiful cabins for rent that overlook the ocean, and a pedestrian walkway takes you directly to the beach. The upper units have the best views, but the lower units are in coastal forests and are on flatter streets (perfect for kids to play or ride bikes).
If you’d rather camp, Harris Beach State Park has wonderful yurts to stay in, but you’ll need to reserve early. Lesser known, Alfred Loab State Park is located on the Chetco River above Brookings, and has riverside campsites. You can access the coastal redwoods there too.
Between Grants Pass and the Coast, you’ll find Out ‘n About Treesort, which has treehouses to stay the night in. Even if you aren’t staying over, it’s worth a stop to try their zip lines. Nearby, Oregon Caves National Monument offers an excellent cave tour, but check to see if your kids are tall enough to enter. As you depart the coast on Highway 199, you should also stop at the CA redwoods (there’s info at the bottom of this post).
Right in Grants Pass, the Jet Boat Tours are fun for kids; they zip along the Rogue River, and some go as far as the ocean.
Enjoy your trip!