Having lived in San Francisco for many many years I can safely tell you there will be no shortage of nice places to shoot.
The Palace of Fine Arts was always a favorite of mine. There is a children's discovery museum right there which is fun if you have younger kids in your family and the surrounding park is very worthy of photographs. Right across the street from the Palace of Fine art is a lot of boat docks and a great view of the bay including the Golden Gate Bridge.
Yerba Buena Center for the Arts is also a nice place. It is sandwhiched between the San Francisco Musuem of Modern Art and the big Sony Center (not sure the exact name these days) so you have both shopping and cultural interests on either side.
Golden Gate Park is always nice if the weather is good.
I honestly don't recommend Haight Ashbury. It's a complete tourist trap these days and very much filled with pan handlers and homeless. By myself I have no problem walking through it, but if I was with a family, especially young kids, I wouldn't bother.
Chinatown in San Francisco is INCREDIBLE. Supposedly it's the largest Chinatown district outside of Asia. I believe it. Lots of fantastic food, things to see, unique shopping, and just great people watching in that district.
Just across the Golden Gate on the north side of the bay there is a lot of nice hiking trails if you are looking for a quite moment away from the hustle of the city. Great views of the San Francisco skyline and the Goldgen Gate bridge can be found here a long with the remains of old military forts which make great photographs.