If you live in Orange County a great place to take your kids is the Pacific Marine Mammal Center in Laguna Beach. It's located on Laguna Canyon Road next to the animal shelter and although it's small, it's worth the trip.
At the PMMC, they rescue, rehabilitate and release seals and sea lions back to the ocean. The kids get a kick out of them swimming in the water and "talking" to each other. It's free to visit but we always try to give a small cash donation. The volunteers there are very nice and helpful with any questions you might have too.