The Aquarium of the Pacific in Long Beach is good and is massive. Scripps Aquarium in La Jolla is smaller but also very nice.Def going to Legoland... not sure about the zoo because took my kid to the one we have here and he was incredibly uninterested. I would go for sure if I hadn't gone before though... but I did.
Kid is into Aquariums. I'm checking what are the best ones in SoCal.