The Pasadena Kids Page web site lists activities for children and families to do in Pasadena. I've looked and seen free music lessons, story hours at the library, concerts, crafts, locations, and times of the Well-Child Clinics and many other things. Exhibits include a TV studio, fire station and beach exhibit. It is basically a giant protected play area with some educational twists- a great place to take your kids.
Hours vary, so call beforehand.
Play groups . These are sometimes listed in the Caltech Calendar . This is great for your kids and not bad for your own sanity. Story times . The Pasadena library system has many story times and is very good about providing stories appropriate for a wide range of ages and interests.