There is lots to do in SF! Cable Cars, Fisherman's Wharf, Golden Gate Park - rent bikes or just go for a walk. The SF Zoo is really nice, there is a carosel with all kinds of animals. The Exploratorium at the Palace of Fine Arts is really fun for all ages. We like to go across the Golden Gate Bridge and hike around the Marin Headlands, there is a Children's Discovery Center over there too. Also the ferries are a great way to see the bridge, Alcatraz, Angel Island and some of the cities on the bay (Sausalito & Tiberon). We rode our bikes on Angel Island and had a child seat for our DD. If you want to get out of the city for a day, a trip to Napa, Sonoma or Santa Cruz are nice options.