If your folks are visiting from out of town, they will almost certainly want to drop by Ghirardelli Square and get some ice cream and/or chocolate. There will be many children and families. It will get cold in the evening and no one will be prepared! If you drive, you will have a hard time finding parking. But it is right near the waterfront, so you can go for a nice walk or just lie down on the grass after all that ice cream!
....and if you think you're pretty smart and know what's what in expensive ice cream...maybe the second time your folks come to visit...you'll take them to fancy California-style ice cream places like Bi-Rite Creamery or Humphry Slocombe and then act real smart when it blows their mind (and empties their wallet). They might even say things like "$3.75 for a tiny scoop! Things really ARE crazy here!"
Finally if you or one of your visiting relatives has a situation where you need to get some Ghirardelli chocolates for someone who doesn't live in the Bay Area, if you can't find any before you or the relatives have to go, you can always buy some at the airport.