Another vote for Morro Bay State Park. No problems with kids and I have some of the loudest ones. They're normal speaking voice is a yell. They love riding around the campground up to the group campsite and speeding down the hill. 
There is a natural history museum within walking distance to the campground and last year was free if you stayed at the campground. We also hiked the black hills trail you can catch it near the golf course or from the campground itself.
Our favorite time was the tide pools at Montana de Oro State Park. Easy hike and go at low tide. My son found a sea star in no time. Don't forget the Morro Rock lots of sea otter's in the bay.
We'll be out there again in August because we had so much fun. This year we're renting kayaks as we just ran out of time.
We have a 34' fifth wheel and it was tight getting into the dump station pretty tight turn for us, but we made it.