"I joke to parents that they need to go into the closet or the shower and practice saying [bleep bleep] a million times to desensitize themselves," she says, referring to a certain sexual act that has become rather common among high schoolers - and even middle schoolers. If you learn the lingo your children are using themselves, or are exposed to, you'll be better equipped to help them navigate the highly sexualized culture, she says.

"You have to use the words, because those are the words the kids are using, and it's letting them know you do get what's going on and you're able to help them with it," says Geltman, who has spoken at several South Shore middle and high schools recently. She's a social worker from Wellesley who teaches classes in child development and the psychology of family life at Curry College in Milton and Lesley University in Cambridge.

Since the youngsters are using language that could come from pornographic magazines and experimenting with "sexting" and worse, Geltman provides parents with a crash course in both the language and behavior. One strategy she suggests is for parents to turn their children into the "teen expert" in the household.

"Parents should say something like, 'Oh my God, I was at the gym today and I heard this story about this kid who sent these naked pictures. Is this really happening?' You speak from the heart, as if you're trying to understand. Then you help your children brainstorm some things they can do to help negotiate these shoals."

The news has been full of stories about "sexting," or the practice of adolescents sending naked photos of themselves via cellphone. Some teens have been charged with child pornography, which seems Draconian to me. I mean, aren't these just children who need to be protected from the real predators? According to one national survey, about 20 percent of teens admit to "sexting."

Doubtless it's because adolescents don't think beyond the period in a sentence. "They just think, this will be fun. They don't think, this will be fun, but . . . " says Geltman. When horrified parents ask their teens the age-old question - What were you thinking? - the answer is obvious. They weren't.

And if we parents think that malls, parties, bar and bat mitzvahs, and sleepovers are safe venues, we're delusional, says Geltman. Sleepovers she calls "the den of iniquities" - parents must be vigilant the entire night. In my household, we've pretty much banned them. My motto to my kids has always been "Nothing good happens after midnight," and that can include inside your own home.

"As soon as the parents' light is out, the alcohol comes out of the backpacks; it's when boys and girls sneak in and sneak out; that's when naked pictures are taken on cellphones and sent," says Geltman. So what's a host parent to do, besides getting up constantly to check on the kids?

In fact, that is precisely what Geltman advises.

"Parents should set their alarm every hour and say to the kids, 'Oh, I have to pee a million times in the night, or I'm starving, I'm up and downstairs a thousand times. I hope I won't keep you up,' " she says. "You might be tired, but when your kid was a baby and needed his 3 in the morning feeding, you didn't say, 'I'm tired, I'm not getting up for you.' This is a part of your job - to keep your kid safe."

To me, a better alternative is to allow your child to visit the host home and stay late, but not overnight. (And beware the ever-popular host home, warns Geltman: It could well be unsupervised.)

Aside from stupidity, it's hard for me to figure out why young girls, in particular, would send nude photos that can be distributed anywhere. But Geltman says they're desperate for boyfriends. And such "boyfriends" are hungry for stories, so there's something each gets out of it, she adds. Getting a "reputation" apparently isn't such a big deal anymore; in fact, it may be a badge of honor in some sets.

At my high school, the most shocking thing boys did was to stand under the bleachers trying to look up girls' dresses. Sure, sometimes things went a lot further and there were girls who got pregnant, but they were girls who were in steady relationships with a boyfriend; a few even got married. There was sex, all right, but it wasn't today's casual sex with various partners. So of course most of us parents remain shocked at what goes on around - or even with - our children.

Kara Russo is the co-president of the PTO at Pierce Middle School in Milton, and brought Geltman to the school for a recent session. Russo, who has two children in high school and one in middle school, was sitting behind the school principal during the talk. "She doesn't hold back on any of the words she uses," says Russo. "And I'm like, OK, she did not just say that."

But it was effective: Many of the parents went home, says Russo, and used those same words and stories with their children. "The shock value they thought was worth it. She made it clear to us that it was our job to educate ourselves about what is going on and not to be afraid to approach it with our children."

In fact, Geltman has been asked to return on April 27 for a question-and-answer period.

A friend of mine who has a middle-schooler and high-schooler sat there listening to Geltman and sinking in her seat. She had assumed she could wait a couple of years to discuss some of this with her younger child.

"But the speaker was great at convincing us to get going," she says. "By the end, I just wanted her to come to my house and talk to my kids for me."

And no doubt, Geltman wouldn't watch her language.

Joani Geltman will speak at the Orpheum Theatre in Foxborough May 18 at 7:30 p.m. Bella English can be reached at english@globe.com.