We like Morro Bay SB, San Simeon SB and Lopez Lake County Park in SLO county.  
San Simeon is great for kids, no hook ups but you will have a better chance of getting in up there.  Lots of paved road to ride bikes and scooters on, beach is within walking distance. Big meadow in lower campground to play in.  We usually drive up to William Randolph Hearst State Beach for day use, its beautiful and there is a kayak rental place that is really fun. Nature museum there too.  Nice little restaurant/wine tasting place next to the beach there too.  
Lake Lopez is dry this time of year but the lake is fun and there are waterslides open till a bit after Labor Day, not sure when they close.  Lots of deer, turkeys, lizards to keep kids busy.
I have an 8 year old boy and he makes friends fast and I hardly see him till dinner. 13 year old is a bit harder to entertain now.
We are camping next week at Huntington Lake and I cannot wait!
Hope you have a great time.