When I used to live in California, my family used to always camp at Leo Carrillo State Beach. The park is located about 28 miles northwest of Santa Monica on the Pacific Coast Highway.
The park has about a mile and a half of beach for swimming which is within walking distance of the park, windsurfing, surf-fishing, and beachcombing. The beach also have really cool coastal caves that kids and adults can hike to and reefs for exploring, as well as tide pools.
The park also features hiking, nature walks, and campfire programs. During the summer the camp also features children's programs.
If you run out of wood for your campfire, then they do have a small store that you can purchase goods from. They also have bathrooms with showers however if you want to take a hot one, last time we were there it was .25 for 3 minutes. Not long but it gets the sand off of you.
We love this camp. Everytime I go back to California for camping, this is where I go.