There comes a time at the end of a long Vineyard summer when the weather loses its sparkle, friends and cousins have all gone home, and kids grow restless. Parents have grown weary of making sandwiches, searching for dry towels, and making another trek to the beach in the fog. The children have been to the Flying Horses in Oak Bluffs and Gus Ben David’s World of Reptiles in Edgartown. They’ve read all the library books about Geronimo Stilton and Captain Underpants. Frazzled parents fight the impulse to give in and let their offspring watch television all day, or lie in bed and play video games until their eyes glaze over.

My daughter, Carolyn, reached this point with her three children last August with ten days left in their Vineyard vacation. Unable to think of any new form of entertainment for her eight-year-old twins, Liza and Zachary, and their ten-year-old brother, Jackson, she loaded them into her van and drove to Menemsha. She had hoped they could while away the afternoon stalking crabs and starfish in the pool by the breakwater. Alas, there were no crabs nor starfish to be found. So the kids began collecting rocks – gray ones, white ones, slightly pinkish ones, striped rocks, and stippled rocks, all of them smooth and rounded – the kind of rocks that fit nicely into the palm of your hand. The children filled their buckets.

At home the next day, Carolyn armed her kids with cans of spray paint and set up production on the patio. The rocks took on glistening coats of blue, red, yellow, and green. Liza said, “We saw some girls at Menemsha selling rocks. But theirs weren’t painted. Ours will be better.” She had already identified a competitive edge.

Soon each brightly painted rock was adorned with a message: MV Rocks, South Beach Rocks, Black Dogs Rock, Red Sox Rock. The words were painstakingly written in black marker. Everything from Obama Rocks to Hannah Montana Rocks. Carolyn moved a small picnic table to the end of our driveway on South Summer Street in Edgartown. I filled a big cooler with lemonade. The kids spread out their wares and taped up a sign: Lemonade 25 cents and Summer Rocks 50 cents.

On that muggy morning in the middle of the week, not many people passed by our house. The hazy sun poured down on an empty street. The thrum of a locust came from somewhere in the treetops. We adults warned the kids that business might be slow. But they had the confidence of youth and the enthusiasm of newly minted entrepreneurs. “When it’s hot, people like lemonade,” Liza said. “When they come, they’ll want to buy our rocks.”

Business was slow at first. Our ninety-three-year-old neighbor came across the street, sampled the lemonade, and bought a rock. Two girls on bikes came by and said they’d be back. I didn’t think they’d return, but twenty minutes later, back they came in an SUV. “We sold lemonade when we were kids,” one girl said. “I’ll take Hannah Montana,” said the other.

Jackson counted the money: “Five dollars and twenty-five cents.” Zachary peered eagerly up and down the street. “Nobody coming,” he reported. The boys grew bored when business was slow. They wandered off to play Nintendo DS, but Liza sat at the table with a book. She seemed to know already that retail is not always exciting, and she was willing to wait. “People will come,” she said. And they did.

“Do you have a rock that says ‘Yankees Rock’?” a customer asked. Liza has grown up in a household of Red Sox fanatics, but she saw the chance for a sale. “We could do a special order for you,” she said with a smile.

Late that afternoon, business picked up. The boys got excited as the money began to roll in. Zachary rushed back to the house for more cups. Jackson took charge of the money. He counted and recounted with every sale. “A lot of people give us tips,” he said. “People are so nice! They say, ‘Keep the change.’”

Inventory was getting depleted. Top sellers were disappearing, as well as some unexpected hits. “Someone bought my Rock Type Pokemon Rock,” Zachary told to his mother. “The one you said no one would buy.” “We need more MV Rocks,” said Liza. “And Red Sox,” Jackson said. “And Pokemon,” said Zack. Clearly the kids knew their market.

Sales continued the following day. Wisely the children adjusted their business hours. “Mornings are slow,” they said. “We’re open three to six in the afternoon. That’s the best time.” Liza developed a spiel. “Come and see our summer rocks – they make good paper weights and souvenirs,” she called out to a passing cyclist. Jackson hit upon the idea of a special offer: “Buy two rocks and get a free lemonade.” Business turned brisk.

They wondered about expanding their territory. “Maybe we could be like the Girl Scouts,” said Liza. “We could go to people’s houses and see if they want to buy lemonade and rocks, instead of cookies.” Her brothers rejected this idea as impractical. It would be too much work carrying rocks and lemonade house to house.

One afternoon I stopped by the sales table during a lull in customer traffic. Zachary, who was peering under the picnic table, discovered a spider. “Look, Liza,” he said. “You can see his eyes.” But Liza was not to be distracted. She had spotted a potential customer: A woman stopped and bought two rocks. “You can have a free lemonade,” the children told her, and they didn’t neglect customer service. “We have a bucket for trash if you drink your lemonade here.” As the woman departed, Liza added, “Thank you for buying our rocks.”

“If people like you, they come back,” she told me. Another important lesson learned.

Then a family approached – a dad herding five little kids. “We need five lemonades,” he said. Then one small boy said, “Look at the rocks,” as he spotted Zack’s new Pokemon design. “No rocks. We don’t need rocks,” said the father. Liza was busy pouring lemonade into five cups. “I need a rock,” said the boy. “That one says Onyx Rocks.” The father counted out money for five lemonades and added an extra dollar. The family moved on across the street. “He gave us extra money,” said Jackson as he tucked the dollar away. Liza picked up the Onyx Rock and called after the boy: “You can have this one for free.” The boy ran back and took the rock from her outstretched hand. Everyone was beaming.

“I love business,” said Liza.

Despite the economic downturn across the country, sales were bustling on South Summer Street. Another trip to Menemsha was needed to replenish the supply of raw materials. There were more runs to Stop & Shop for lemonade and to Granite Hardware for paint. The profits were mounting: $55.00, $76.83, $98.50, and then came the magic breakthrough – $100.03. With this rate of success, anything seemed possible. “Maybe the president will come and buy a rock,” said Jackson. President Obama didn’t arrive on the Island in time to buy a summer rock, but a famous Harvard professor stopped by one day and made a purchase.

At the week’s end, the kids were down to their last few rocks. Their mother was packing to leave the Island, and Jackson reported that they now had $149.60. They set up the sales table for the last time. By the end of that afternoon, the cooler was empty, the rocks were almost gone, and they had sold $155.00 worth of lemonade and summer rocks, all clear profit thanks to their backers, who donated paint, lemonade, and transportation.

“Will you be here tomorrow?” asked a cyclist who was gliding past as the kids were packing up. “Not tomorrow,” said Zack.

Liza called out, “Wait till next year!”