Well - at California Adventure, you can't miss Soarin' Over California, and at Disneyland, I would say the show Fantasmic! . Soarin' is a ride, very family friendly, and I'd say it's the best ride Disney has come up with. And Fantasmic is just plain amazing. If you're going when Fantasmic! may not be playing, then the must see at Disneyland, for my famly, would be the Indiana Jones ride. There are MANY other things, but none of these can be found at Disney World. A different version of Fantasmic plays at MGM, but it's not as good as Disneyland's! Also - don't miss the Redwood Creek Challenge Trail at CA ADV. Some people skip it because it isn't a ride - but we love playing around there. I'm jealous! Have fun!
If I have to pick just one thing not to miss......whatever you do, dont miss seeing Fantasmic! It is an amazing show. The sweetpea loves it and is almost all she talks about when we go to DL.
Do not miss the Aladdin show in Cal. Adv. - I don't want to spoil it, but all I can say is I am a theater person who loves broadway shows - and this blew me away! It is not a hokey little show like some might expect!