Monterey also has the Dennis The Menace Park, which might be as much fun for the little ones as many of the more scenic options. The aquarium is great, with a ray-petting pool and lots of cool sea life.

Sequoia and Kings Canyon NP are along the inland route off Highway 99, as is Yosemite. In July, Yosemite will be near impossible for the crowds. Sequoia/KC will be a bit better but still crowded. If you go, I suggest some time for a little hike along one of the nature trails so the kids can play near the water and look for animals. Accommodations can be found in Visalia or Fresno, an hour or so down the hill from the parks.

For the coast route, Hearst Castle would be a bore for the kids but the elephant seal viewing area nearby might be a big hit, as would a walk on the San Simeon Pier or some play time in the sand.