If this is going to be your only trip to California and you have an extra 3 days, I would definitely devote one of them (a full day, from morning until evening) to Catalina Island/Avalon. It's a beautiful place and it makes a great day trip. Renting a golf cart and buzzing around Avalon is a lot of fun. Some of the tours are interesting too.
You could take the Catalina Express out of Long Beach (which has the most departures and return times), and Long Beach is maybe 20 or 25 minutes away from Anaheim, without traffic.
At the bottom of my signature below, there is a blue link to my Catalina Island day trip report from last July. It's not a long thread - maybe 4 or 5 pages at most - and it is full of comprehensive photos taken around Avalon! Maybe the photos will give you an idea of whether or not this looks like something your family would be interested in.
Another idea might be to visit the Aquarium of the Pacific in Long Beach (very close to where the Catalina Express landing is).
Then there is the La Brea Tar Pits and the Los Angeles County Museum of Art, (LACMA), which are right next door to each other in Los Angeles. A few minutes away from LACMA and the Tar Pits are the original Farmers Market (lots of great food) and The Grove - a very nice shopping center where celebrities are often spotted. You could make a whole day of seeing LACMA, the Tar Pits, The Grove and Farmers Market.
There is also the Disney Studio Store and Soda Fountain on Hollywood Boulevard.