This is a public event that's open from 10am to 4pm.  My family is planning on going around 10/10:30a.  We've been attending this event since my son was 3-4 year old. Most exhibits are targeted for 9-12 years old, but all children and adults are invited.  The Children's Museum of Sonoma County will have a booth for younger kids.  Last year the boy scouts had an ice cream making booth!

More info HERE.