You have to go to Fern Canyon. Parts of Jurassic Park were shot there and it is a great easy hike up through the canyon. My kids love it there and still talk about it (they are in college). The road to get there is about 6 miles of gravel road, through a couple of creeks, but it is well worth the trip. There is an elk viewing area as well right were you turn off 101.
Not sure when your are traveling, but the weather is currently wet windy and cold. Dress accordingly.
Harris Beach in Brookings is a great beach for kids but can get pretty busy. We like the beach in Harbor by the Best Western - lots of logs, sand, rocks, and tide pools down a ways when the tide is out. It is easy to find enough wood to make a fire. This Best Western is also a great place to stay since it is right on the beach (and they take dogs).
As far as food, you are on your own. I have spent a lot of along that area and can not recommend a single restaurant (that I like) north of McKinleyville other than the pancake place in Brookings/Harbor where the turn is to go down to the Best Western. We usually go to the market and get bread, meat, cheese, and wine to enjoy on the beach (weather permitting).