Don't expect to see the whole city from pedal-powered transport, though. Unless your whole family are avid bikers and strong pedalers, you'll be limited to the waterfront and other flatter parts, but there's plenty to see there, including many of the most popular tourist spots.
Families on Wheels - Most Popular Spots
For an active, do-it-yourself tour of San Francisco, rent bicycles from Blazing Saddles, Bay City Bike or Bike and Roll. They'll give you a map with several route ideas, the most fun being a two-hour ride that will lead you over the Golden Gate Bridge to Sausalito and back on the ferry.
If you like the idea but worry about wearing yourself out, Blazing Saddles and Bay City Bike also rent electric-assisted models. All three have tandem bicycles, tag-a-longs and trailers. And most have baby seats.
Ride a Segway: If the kids are old enough (over 12), the San Francisco Electric Tour Company offers fun tours on Segway personal transporters. They'll give you a lesson and then take you out to see the sights. Get all the details - and a review - here.
More Places to Bike, Skate, PlayIf you'd just like to pedal around the Crissy Field area, Sports Basement rents a nice range of bikes at their Presidio location, and their rates are significantly lower than the places in the more-touristy areas.
For a nice ride in Golden Gate Park (a great idea on weekends when some of the roads are car-free), try Golden Gate Park Bike & Skate where you can choose from bikes or skates - and even rent a disc golf setup. Also in the park, Wheel Fun rents a dizzying array of wheeled vehicles, including some really cute pedal-powered surreys.
If you take the ferry to Angel Island, you can take a Segway tour there, rent bicycles or try a fun, electric-powered scooter.