Many couldn't understand what all the "commotion" is about. One commenter on New York magazine's Web site declared, "All I can see are beautiful people having a good time…It's not the advertising that makes little children confused, it's the uptight handling with sex-related issues in general of their parents."
Even those who have never considered a ménage a trois (or more) don't seem shocked by the notion that more is merrier.
"I think that many younger people are OK with threes and fours, theoretically," said Lauren, a 28-year-old New York City teacher who did not want her last name used. "In college, many people engage in threesomes either with three friends, strangers or even their main partner and then a friend."
But some say Calvin Klein, whose earlier ads seem tame by comparison, has hit a cultural nerve.
"It's just porn from a guy who's done kiddie porn," said Bob Garfield, ad critic at Advertising Age and co-host of National Public Radio's, "On the Media." "If you pay attention to it, you're just doing his advertising for him."
Even the New York media -- accustomed to the bare midriffs that adorn Times Square -- has looked down its nose at the sexual implications of the four semi-nude models on the billboard.
"There's no such thing as a foursome," chided the Daily News. "Anything over three and it's called orgy."
That remark, said Ashara Love, a 51-year-old who belongs to Loving More, a Colorado-based organization that promotes polyamory, reflects society's disapproval of more sexually free attitudes.
Polyamory is a "gender identity" not a lifestyle choice, according to Love, who said she does not use her birth name to protect her parents, who do not know she is "out."
"With cultural imperatives, the mainstream media frequently reinforces what you should think," said Love, who is happily married but engages in threesomes. "Hey guys, it's over there, pay no attention, it's just an orgy."
What critics are upset about, according to Love, is the unusual combination of one girl and three young men.
"Everything about our arts and culture is homoeroticism and denial," she told ABCNews.com. "What men are really afraid of is having sex with another guy. That's what's scaring people."
But Love and others, say the brilliance of Calvin Klein is his ability to tap into the next wave of shifting attitudes -- especially among those who buy their products.
"He reaches young kids at a place where they are and opens them up even more," she said. "Everyone is really comfortable. They are having a good time, no wink, wink, nod, aren't we naughty for doing this. Everyone is completely in the moment and it's extremely confronting for people. It pushes the cultural input button."
But media observers say the issue is less about censorship and more about "media sanity" and what is age-appropriate.
"I can guarantee everyone below Houston Street [in Soho] is having a conversation with their children right now," said Liz Perle, editor-in-chief of Common Sense Media, a nonprofit that provides ratings for parents.
"It's just not age appropriate for kids who haven't even kissed a boy to be introduced to sophisticated, mature behavior," Perle told ABCNews.com. "They are not emotionally ready to deal with that yet."
Common Sense Media works with Time Warner, Best Buys and Netflix to help families "make better decisions."
"We are not negative Nellies," she said.
That Calvin Klein billboard -- towering over a community that is now more child-friendly -- is a reminder that the age of the Internet has changed a child's perception of the world and "normalizes" highly sexualized content.
"Childhood used to be about a system of revealed secrets that are learned when they are ready to handle them," said Perle. "Our society is so desensitized that we have in-your-face violence and in-your-face sexuality."
"Here [in the billboard ad] are these beautiful people engaged in activities that are not age-appropriate for kids."