If it comes to a choice between California Adventure or Disneyland: definitely go to Disneyland. Knotts Berryfarm would be almost last on my list of theme parks to visit, but that's just me.
I have only been to California Adventure once, and that was plenty. I have no desire to
ever pay to get into that place. I had free passes the one time I did go, so at least I didn't feel like I was ripped off. The best part of my day there was the long, wonderful lunch I had at one of the restaurants (which isn't even there anymore).
If you are interested in seeing a movie studio while you are in Hollywood, you could check into taking a tour at the Warner Brothers lot in Burbank. It's literally on the other side of the hill from the Universal Studios theme park and it is a real, working studio as opposed to a theme park. Yes, you can take a tram tour of the Universal Studios back lots where some movies are filmed, but Warner Brothers is not as tourist-y IMHO. However, your younger kids might not find a studio tour very interesting.
Another theme park somewhere in SoCal is the LegoLand Adventure park. I really don't know where it is, but from all the commercials I've seen it looks like a great place for the little ones. Lots of interactive rides, and fun kid-oriented stuff.
If you are looking to witness a little bit of the nutty SoCal stereotypes, a visit to Venice Beach is a must on a weekend. There are plenty of street performers, artists, and crazies out there to see.
When you are in Hollywood, be prepared for the costumed characters all over the place. They will pose for pictures with your family, for a price naturally.