De Young Museum
Japanese Tea Garden in GG Park (across from the DeYoung)
Palace of Fine Arts (next to Exploratorium)
Golden Gate Bridge
There's a lookout area (Vista Point) on the N side of the bridge (only accesible to N bound freeway traffic). There's also a lookout area up on the mountain on the other side of the freeway from Vista Point. Great views of the city from both.
Of course, there's Union Square, the Cannery Building (near Ghirardelli Square), the Cable Car Museum. If you want to ride the cable car, the line is usually shorter on the Ghirardelli/Fisherman's Wharf end than the Union Square end. There's theatres and plenty of restaurants.Only in SF
is a decent tourism website.
If you're looking for food, I'd suggest checking out Chowhound, and asking for suggestions... be specific in your request, do you want seafood, steak, chinese, etc... and how much money you want to spend and the ages of children you will have with you.
You can also always take the ferry from Embarcadero to Oakland and/or Alameda to check out those areas for a few hours, or you can take the BART from Market to any number of places in the E. Bay. You can also take the ferry to Sausalito and check out that area.
There's lots to see and do, it's a matter of how much time you'll have and how much money.
On the weekends, outside Ghirardelli Square, there is a street market, handmade jewelry and art and that kind of thing.
If you want to do a vineyard tour, that's liable to be an entire day expedition, since the drive alone is about 90 minutes-2 hours each way.
And if you want to see Alcatraz, I highly suggest buying your tickets in advance, they are rarely available at the ticket counter.
Something most people don't realize is that Pier 39, Fisherman's Wharf, Ghirardelli Square, and the Cannery Building is all in a nice little row (along with the ferry piers for ferries to Angel Island, Alcatraz and Bay Tours). You could probably walk to them from Union Square, if you don't mind climbing up and down the hills (it's a straight shot, but about 2 miles, I think). They are all very close to eachother, but it is a lot to see in 1 day. If you're looking for food, I don't recommend any of the restaurants at Fisherman's Wharf, they are all pricey. I do recommend the street stands, especially if they're cracking crab. A stop at Ghirardelli is a given, so arrange to get there for dessert (whether it's chocolate or ice cream).
Oh, and I know you're traveling in the "summer", but bring pants. And jackets. It is currently 55 degrees, and there's a nice breeze. Natives can always tell the tourists because they're the ones wearing shorts and sandals and bundled up in overpriced sweatshirts they had to buy when they realized they hadn't packed properly. (Of course, now that I said that, we'll have a heat wave while you're in town.
Feel free to PM me if you want any more specifics or would like a few restaurant recommendations.