1 Jelly Bean Lane in Fairfield, CA.
http://www.jellybelly.com/visit_jelly_belly/california_factory_index.aspx
Free 40-minute walking tours run daily from 9:00am – 4:00pm. and depart every fifteen minutes. Weekdays are definitely less crowded than weekends, but there is a large café and waiting area which have plenty of distractions for kids. Also on weekends the factory is closed, so the tour includes video of the machines at work. Its a little less exciting than watching employees at working machines with beans whizzing by on conveyor belts, but still a worthwhile tour. Participants get a free hat (which must be worn during the tour) and a sample packet of jelly beans.
You can also sign up for a private small-group tour, the Jelly Belly University tour for $47 per person, where you get a 75-minute tour on the factory floor (instead of the plexiglassed platform above), get to see each step of the process of making jelly beans and other candy, more sampling, etc. To do this go directly to the information desk by the gift shop rather than waiting in line. The tour costs $40 for adults and $30 for teenagers. ($45 per person?) Participants must be over six years old. In addition to the free hat and samples, you also get a free t-shirt and a 10% coupon for the gift shop / food area afterwards.