I did the San Fran trip about 6 years ago, in the city I didn't have much luck with family photos compared to 1-2 hours North (along coast and Sonoma) and 1-2 hours South (Carmel area). Chinatown is amazing as others have mentioned, but the coastal areas are incredible with the vistas in about any direction.
It is fun to have afternoon sun coming from the water and the rugged coast as a backdrop, lots of kids running towards the waves on shore, and back, etc.
I don't remember where you will be coming from, but a sweater and jacket(s) in No. Cali in August are suggested.