Like kids have done during the summer for time immemorial, 8-year-old Vivienne Harr of Fairfax has been selling lemonade at a little stand she sets up in her neighborhood. But Vivienne’s stand is unlike any other. She calls it her “stand against slavery.” And, as of Saturday afternoon, she’s made more than $30,000.

The money from Vivienne’s Make-A-Stand! Lemonade: The Sweet Taste of Freedom,” and its online equivalent, www.makeastandlemonade.com, goes to a Half Moon Bay-based nonprofit called Not For Sale, whose mission is to fight human trafficking and modern-day slavery around the world.

Not For Sale was founded in 2007 by David Batstone after he discovered that the Indian teenagers working in his favorite Bay Area restaurant were slaves, and the place was the center of a human trafficking ring.

The Harr family became conscious of this shadowy issue while on a family trip to Sonoma. They were browsing in a gallery when they began leafing through “Slavery,” a coffee table book by Lisa Kristine, a journalist who photographs enslaved people around the globe.

“Here we are this Marin family and we were blissfully unaware that there are 30 million slaves in the world, half of them children, and 100,000 are in the United States,” said Vivienne’s father, tri-althlete and author Eric Harr. “We were embarrassed and ashamed that we didn’t know about this.”

One particularly poignant photo in the book, of two little enslaved boys holding hands, jolted them into taking action. They decided to raise $150,000 for Not for Sale. But how?

“At first we didn’t have an idea,” Vivienne said on Saturday afternoon as she and her parents and 3-year-old brother, Turner, set up her stand in a Fairfax park. “So I said, ‘Maybe we can sell lemonade.’ My parents said, ‘Honey, that’s a lot of lemonade.’ But after they thought about it, they said, ‘Actually, that could very well work.'”

And they were right. Saturday was the 56th consecutive day that Vivienne has sold the all-organic, fair trade lemonade that she and her family make at home using agave nectar as a sweetener. Fresh mint and raspberries are optional.

“It’s been really great, especially for a Marin kid, to do something inconvenient and selfless for at least an hour every day,” her mom, Alexandra, said.

At first, Vivienne charged $2 a cup for her lemonade, but now leaves it up to her customers to decide how much they want to pay.

“We’re betting on the goodness of people, and we found that the average price went up $18 when we made it free,” her dad said. “We said, ‘Pay what’s in your heart.'”

While she works, Vivienne often listens to music by pop star Katy Perry, one of her 15,000 Twitter followers. Another is New York Times columnist Nicholas Kristof, who tweeted about Vivienne’s stand, generating more than $18,000 in donations in 24 hours.

“That’s the beauty of social media — an 8-year-old can communicate with a New York Times columnist,” said her dad, who runs his own social media company.

Most of the money has come from donations to makeastandlemonade.com. But Vivienne and her family plan to continue selling on the street until they reach their $150,000 goal, and maybe even after that.

Fred Schultheis, a 61-year-old high-tech businessman, was Vivienne’s first customer on Saturday, stopping his pickup truck when he saw the stand.

“I’m totally touched by this,” he said. “This is a very kind thing to do.”

Alba Moreno also pulled over, buying lemonade for herself and her 5-year-old daughter, Maia.

“It’s very important that young kids become aware of what’s going on around the world and do something to help people,” she said. “It’s what we should all do, not just kids.”

Contact Paul Liberatore via email at liberatore@marinij.com