Kids around the Bay Area [1] have loved the Exploratorium (3601 Lyon St., www.exploratorium.edu [2], Tues.–Sun. 10 a.m.–5 p.m. plus some Mon. holidays, adults $14, youth and students $11, children $9) for decades. This innovative museum makes science the funnest thing ever for kids of all ages—though adults are welcome to join in on the interactive exhibits too!
Here you can learn about everything from frogs to the physics of baseball, sound to seismology; the Exploratorium seeks to be true to its name and encourage exploration into all aspects of science.
For an utterly unusual experience, pay an extra $3 and walk bravely (and blindly) into the Tactile Dome, a lightless space where you can “see” your way only by reaching out and touching the environment around you.
Links:
[1] http://www.moon.com/destinations/california/san-francisco-and-the-bay-area
[2] http://www.exploratorium.edu