Most people only walk halfway across the bridge, but if you push yourself, you can see it's really not very difficult. It's free to cross and you can get there by bus. Once you get to the top of Vista Point, it is such a breathtaking view, it's all worth it. Walking back the bridge is easier than walking across it the first time. Although you feel like it takes forever and it is impossible, you feel a huge sense of boastful accomplishment. On the top of Vista Point (which only takes 15 or so minutes to walk), there is Battery Spencer. You don't have to cross it, but I found it to be creepy and spooky. It is an old watch point for the Bay and a temporary prison for those being transferred to Alcatraz. Vista Point is hardly worth avoiding for it, though, because the view from the top is my favorite. I would not, however, suggest taking your children all the way across the bridge, as it might be torturous to endure the complaining...
Golden Gate:
http://www.goldengate.org/
Vista Point:
http://www.lovetoeatandtravel.com/Site/Sfbay/SF/Fun/ggbridge.htm
Battery Spencer:
http://www.militarymuseum.org/BtySpencer.html
http://virtualguidebooks.com/NorthCalif/MarinNorthBay/ConzelmanRoad/BatterySpencerTop.html