There are a lot of awesome things to do in California, this is the list of what I believe are the best theme parks.
Disneyland is probably the most famous theme park there is. It's located in Anaheim and also has California Adventure And Downtown Disney attached to it. Not to be taken lightly, you will be there all day to get to all the rides that you want. Because of the amount of time spent there, make sure you rest often, eat and keep hydrated. Take a lot of pictures. It's a good family experience.
Knott's Berry Farm is located in Buena park. They are not as big as Disneyland but they are still fun. They have mostly a western theme there. You can dress up like a cowboy or cowgirl and get old style black and white photos taken. They have stunt shows and you can ride a train around the park. They have rides and they have plenty of places to eat at there.
Universal Studios is in Hollywood. Their theme is rides based on different blockbuster movies. Most of the rides are not too intense but they are still fun. They make you feel like you are in the movie.
Legoland is in Carlsbad which is close to San Diego. They have plenty of rides there. Their theme is for a family with younger kids, but everyone can enjoy the park.
Seaworld is in San Diego. If you are not the type of person that likes getting on a lot of rides, Seaworld is good. It has a lot of shows and you can can observe the different sea animals and learn about them. Kids and adults both really enjoy this park.
Because all of these parks require a lot of walking make sure you dress comfortable and bring sun block as you will be outside most of the time.
I haven't been for years but I would have found a spot for Magic Mountain on the list :) I've been to all except Legoland...my oldest grandkids are almost three...so they are getting close to the age to go :) H5
select one here...