Weekend at Russian Gulch State Park
Russian Gulch State Park near Mendocino offers a low key, compact, but very clean and quiet campground for families. Beware that the place has no cell or data connection of any kind (which worked out great) but offers great access to awesome sights and walks.
The path from the end of the campground leads to a very nice walk leading up to a waterfall. I don't recall the hike well (I did this one last year) AllTrails shows it's less than 4 miles.
Mackerricher State Park
Dinner: Silver's at the Wharf, Sea Pal Cove
While we love cooking outdoors, I wouldn't miss out an opportunity to enjoy good local eateries. The two I liked are Silver's at the Wharf that offers good old American dishes (prime rib, fish and chips...):
...and Sea Pal Cove, which is super casual but kick ass fish and chips.
I kick myself for not taking food photos from either place, but Google Maps should have plenty of those too whet you appetite!