I'm not sure what your budget is, but here are a few ideas.
For a tight budget, I would suggest coming down to the Santa Cruz/Monterey area. The aquarium is amazing! There are also museums that are interesting for kids, several great parks, and The Boardwalk. There is also a great swim center in Santa Cruz with a waterslide and kid pool.
A week in San Diego is also a great choice. Tons for families to do there.
The las suggestion I would have is a Carnival cruise. They are amazingly affordable and have lots to offer for all ages. My kids loved the cruise we went on when they were 4 and 6, and also loved the one we took just last year at 13 and 15. Once you look at what all is included, it really is super affordable. Carnival is very family oriented, so it would be my choice with kids. Disney also offers cruises that my friends say are fantastic, but they are WAY more expensive and our family decided we'd rather save that money for shore excursions with Carnival. My girls have now swam with dolphins twice! Unforgettable experience!