Our littlest one is almost six, and he hasn't been since he was a baby. Now that all but the youngest are "adults" -- meaning 9 and up -- it costs a small fortune for the six of us to go. I'm hoping to get him there this year anyway, as it is such a magical age.
I'll freepmail you with a page of Bay area attractions, in case you are interested.
Thanks, that would be great!