My oldest daughter and I were walking around San Francisco's SOMA neighborhood on a clear autumn day in search of a mattress store called Keetsa back in 2008. I remember turning a corner and almost bumping into an enormous naked man riding his bicycle on the sidewalk.

My daughter was five at the time and she was startled.

"Mom, why does that guy have a sock on his penis?" she asked.

"Um, well, um..."

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"Why are there rings sticking through his bottom?"

Walking further down the sidewalk, we passed men wearing black leather chaps with their rears fully exposed and a few more naked guys.

Suddenly it clicked. We were on the outskirts of the Folsom Street Fair, the annual BDSM and kink fest that takes over SOMA's Folsom Street — and I was at a loss for words.

"Mom, why are these people like that?"

"Ummm..."

The festival is taking place again this Sunday, Sept. 29, 11 a.m. to 6 p.m., and so you don't find yourself in the same situation — shocked and tongue-tied — here are some tips.

Don't bring your kids to the Folsom Street Fair

Think that taking your kids to the fair might be an enriching cultural experience? Think again. The Folsom Street Fair has an official policy against kids attending and here it is:

Please do not bring children less than 18 years of age to our street fairs; the environment is very much for adults only. If you want to "expose" your child to alternative sexualities, there are other ways to do it – read a book, watch a movie, or attend a conference. Our gates and security volunteers will stop you, discourage you from entering and reinforce our policy directly with you (repeatedly). Find a babysitter; and, enjoy a day with your adult fetish friends.

Steer clear of the SOMA area on Sunday

"We actively avoid getting anywhere near it," says San Francisco mom Julia Nishihira Damir, who's raising two boys in the city. "No Costco runs, no restaurant runs in the southeastern part of town. Every family has their thing; this is just ours."

This year's festival runs along Folsom, between 8th and 13th Streets. A few nearby businesses and places to avoid visiting include Costco, Victoria Manalo Draves Park, and the Trader Joe's and Bed Bath & Beyond at Showplace Square — oh, and, of course, Keetsa.

Know what to say if you accidentally bump into costumed (or naked) Folsom festival-goers

I said more than "ummm" when my daughter asked about the man with the sock on his penis, but my bumbling explanation isn't anything to offer up as an example for other parents.

To help those families who bump into enthusiastic festival-goers on the the BART train, in the Costco parking lot, or crossing Market Street, I checked in with some friends who've learned how to talk to their kids about adults wearing unusual costumes or no clothing at all. Geoffrey Benjamin and Craig Persiko are raising kids in the heart of the Castro.

"Living in S.F., our kids are used to seeing special costumes and special events," says Persiko. "We tell them this one is for adults only, in a way that some adults like to play dress-up and pretend. I also talked about it that way when our kids asked about store displays in the Castro with mannequins in handcuffs."

Benjamin adds that kids' brains aren't wired to understand the point of a man dressed in black leather. The Folsom Street Fair is about sexual titillation for adults, and for kids who haven't gone through puberty, the costumes and nudity simply don't make sense. "I'll tell my kids that their bodies aren't ready to understand those costumes," he says.

While Benjamin doesn't recommend taking children anywhere near the Folsom Street Fair on Sunday, he does think parents need to have longer discussions with their children about sexual things.

"At some point it's going to come up," he says. "You have to break it down for them."

"I start by explaining puberty and that when their bodies are ready to have sex they will notice things in other people that may make them think of sex," Benjamin says. "For people who've been through puberty, sex feels really good and thinking about it can make you think about that feeling.

"For some people naked bodies make them think about sex, for other people it's sexy underwear, and for others it can be certain clothing like black leather. Folsom Fair is for a community of adults who like black leather. It makes them feel good."

And for those who aren't convinced the Folsom Street Fair isn't a good place for kids, check out SFGate's photo gallery above to get a taste of what goes on there.

Note: This story appeared on SFGate in 2014, and we're republishing it with a few changes.