Niles Canyon Railway
You could consider a train ride somewhere. We had a 2-year-old birthday on the Niles Canyon railway and a 3-year-old birthday riding Amtrak to Sacramento (to go the train museum). Or meet up a museum that both adults and kids would enjoy, like Cal Academy of Sciences or the Oakland Museum of California.
Archived Q&A and Reviews
Re: birthday party for 6-year-old
The Niles Canyon Railway in Sunol runs trains every Sunday during the Spring and Summer and on the first and third Sundays of the month during the Fall and Winter seasons. It's a fun ride for the whole family. If you have a larger group, I think you can call and book reservations in advance. The full-sized train runs through the small town of Sunol, and the kids love it when the train gets to toot its whistle in warning to cross the streets and people wave, and then it winds its way through the canyon. In the spring, the wildflowers are out and make it a very pretty ride. The conductors are all friendly and knowledgable. There's usually a covered car and an open car, so you can take your pick of sunshine (remember what that is??) or shade/cover from the rain. If you're making a party of it, they might be able to recommend some nice picnic spots nearby the train depot to have treats. It's a bit of a drive from Berkeley (45 mins - 1 hour), but if you are just inviting a few of his friends along and making an outing of it, it could be fun. Information at: http://www.ncry.org/ncryxcur.htm