The multiple museums in downtown Los Angeles do not get quite as much attention as the other attractions in Southern California, but places like the California Science Center prove there are more things to do for families with younger children than just Disneyland.
I was surprised at how much I enjoyed the Science Center, even though I am older than twelve, which is a good sign for a family attraction. Plus most of the exhibits are free. Some of the seasonal exhibits and the most popular attraction, the Space Shuttle Endeavour, have some fees attached. Since the Space Shuttle is the most popular attraction you have to reserve a specific time to visit the exhibit and it may be harder to reserve on the same day you plan on visiting.
Science museums are usually more entertaining than other types of museums since the exhibits are more involved and include visuals, sounds, and hands-on aspects that other museums(looking at you art museums) do not always have. More specifically, the California Science Center has a lot to offer, from ecosystem exhibits, to exhibits about the human body, and many air and space attractions.