Here are a few handy tips for families:

Playgrounds -- kids need playgrounds, no matter where they are.  There's a great playground in Chinatown, called Portsmouth Square, at 733 Kearny (with a parking garage underneath).  There's a great Chinese restaurant (well, there are a ton of them, but this one's really popular) just a block away called R & G Lounge.  Another fun playground is at Yerba Buena Gardens, just across Mission from the Metreon (which is a city block bordered by 3rd & 4th, at Mission).  Besides the playground there's a carousel ($3/person for 2 rides; closes at 6 p.m.) and some other fun things for kids (carousel, ice skating, etc.).

Unusual museums and attractions -- when you go to Fisherman's Wharf, be sure to check out Musee Mechanique, a collection of genuine (old!) penny arcade games, and a few vintage video games.  There's something for everyone here.  Games cost a quarter, not a penny, but it's still cheaper than most attractions in San Francisco.  Right next door is the USS Pampanito, a World War II submarine -- buy the audio tour.  Further down Fisherman's Wharf, almost to Ghirardelli Square, is a small maritime museum.  Not the big white one just past all the ships; this is a smaller one next to the Argonaut Hotel.  It's free, and has some great displays.  Be sure to check out the continuous-loop movies they have about maritime history.  There's one about women mariners, and one that's actual footage of a masted sailing ship rounding Cape Horn.  Another great museum is the Boudin museum and factory tour -- right there on the Wharf.  There's all sorts of history of SF, including how the Gold Rush played into the success of the Boudin bakery.  Lots of science, too, about how the starter works, how yeast rises, etc.   There's even a computer game you can play (though they don't give you a free loaf if you win anymore), and bread tasting when you're done.  And Boudin is a great place for lunch on Fisherman's Wharf -- great sandwiches, fast service, plenty of seating.

 While you're in Fisherman's Wharf, buy a jacket.  They have so many jackets for sale, for really cheap prices.  And they're good!