When my kids were little we used to do a lot of camping and it is a really great way to travel with little kids. They love it and are entertained with just exploring the campground and playing in the mud. They were always very dirty and sometimes the only way we had to clean them up was in a big bucket so I have some great pictures of my husband standing one of them in a bucket and washing them. I will have to get them scanned in so I can post them someday.
Anyway one of our favorite trips was to Big Sur.
Check out this website for more pictures and camping information: http://www.bigsurcalifornia.org/camping.html. There are campgrounds owned by the State Park system and some that are run as a private business. This is another camping spot where I would suggest making your reservation well in advance of your trip because it is very popular.
It can get quite cold at night even in the summer so bring a good sleeping bag and warn clothes. You can do a lot of hiking and exploring and this is where you will find Redwood trees some of which are well over 300 feet tall and something everyone should see at least once. The kids will be in awe.
I would also suggest eating at the Nepenthe restaurant which is located on Highway One. We went there and our oldest child (8 at the time) was totally shocked with the view as were my husband and I (the 2 year did not really care). Below is a picture of one of the views you will see there. I got the picture off the home page, http://www.nepenthebigsur.com/. Go to that page and you will get all the info you need. We had to wait over an hour so I would suggest going early or seeing if you can make a reservation..
Have fun and make sure you go to the restaurant. And one other interesting fact about the restaurant is that it was designed by a student of Frank Lloyd Wright, his name was Rowan Makden.