For San Diego our family favorite, for more years than I can remember, has always been Campland On The Bay. Large, rustic campground with family, children activities planned all day long. Enclosed, with only one road in or out makes it a great place to let the kids run off by themselves. Many playgrounds, lovely bay beach, boat rentals, bike rentals. We try to get there almost every year, previously with the kids, not with kids and grandkids. San Diego KOA is also a gem in the KOA group. Our first choice has always been Campland.
There are a few parks near Disneyland. All offer shuttle service. None are much to talk about. Just clean parking lots with hookups. It is expected that you wake up early, head to the park, stay till late, and come back to sleep.
There is no end to LA traffic. Either head out after 10am before 2pm or stay for dinner and leave after 8pm, and you will still hit traffic. Take any road, a bit out of the way, to catch the 210. Up the 57, or 5 to the 605, or if your lucky you can stay on the 5. Your goal is to get to the 118 North. The 118 with go through Simi and turn and become the 26. The 26 will reach the 101 in Thousand Oaks near Oxnard. The head up the 101. You may hit traffic between Oxnard and Ventura, then it will open up as you drive by the Ocean until Santa Barbara, where it will be congested through the small city. Then wide open again. In Buelton, near Solvang, on the 101 is Flying Flags RV Resort. Wonderful place to stop. Large grassy sites, big playground, nice pool, children friendly. Walking distance from FlyingFlags is a little whole in the wall restaurant, Ethel's I think, grey building across the street from the Windmill. Fantastic food, historic, been there for ages, great for breakfast or dinner. If you want to stay on the 101 then Santa Cruz KOA is a great stop. Otherwise you head east on 46 to pick up the 5. Not much to look forward to on the 5.
Happy Trails.