Transamerica Pyramid. Can't have San Francisco photos without one of the Transamerica Pyramid. Nearby, there's also the Embarcadero and that funky Hilton with the rotating restaurant on top. Bay Bridge is right next door, too.
There's Chinatown, the Embarcadero, Fisherman's Wharf, Exploratorium, Palace of Fine Arts, the fog, and, of course, cable cars. The cable car turnaround at Powell/Market might be fun. Golden Gate Park is huge if you wanted things botanical. Alcatraz with a 3yo in tow might not be the best idea.
And there's always
Lombard Street, although that's a difficult one to tackle photographically if you're actually
on it.
If you've got a car, and you want a fantastic skyline of the City, take the Bay Bridge (heading towards Oakland) and stop off at Yerba Buena and/or Treasure Island. You can get the most amazing vista from out there.