The days of setting up a lemonade stand to make money during the school holidays could be over forever, with two US siblings pulling in US$30,000 per month by cryptocurrency mining.
Texas-based Ishaan Thakur, 14, and his nine-year-old sister Aanya spent their summer learning how to turn a single gaming computer into a big-bucks business - and have become so successful they've had to move their rigs to a professional data centre.
"We started because we wanted to learn something new - and also make some money along the way," Ishaan told CNBC.
"We could have spent the entire summer playing video games, but instead we used our spare time to learn about technology."
And that's set to land them around US$36,000 in September based on the equipment they have and what's on order.
Currently, they have around 97 computer processors doing the calculations necessary to mine cryptocurrencies, with many of them Nvidia RTX 3090 graphics cards.
Each of those cards cost between US$2500-3000 to buy, with their dad Raj, a former investment banker, helping to fund the business with a loan.
The duo currently mine for bitcoin and ether - the two largest cryptocurrencies by market value - as well as ravencoin, a less popular altcoin.
Bitcoin, in particular, has been widely criticised for the negative environmental impact of mining.
Dr Tara Shirvani, who works for Autonomy Capital as an expert in disruptive technologies and sustainability, says bitcoin alone could generate enough carbon dioxide to push global warming beyond 2C by 2033.
"Current global energy consumption for service to run bitcoin software is around 22 terawatt hours per year. That's the same amount of energy consumption a country the size of Ireland has," Shirvani said.
The environmental impact of bitcoin was also the main reason Tesla CEO Elon Musk cited for withdrawing it as an option to pay for one of the company's cars.
And while the brother and sister say they use 100 percent renewable energy for their mining at home, the majority is done at an offsite data centre.
"We moved from my desk to the garage, since the house was getting too much heat and noise. We now use the garage only for building and testing mining rigs. When they are ready, we move them to a professional, air-conditioned data centre in downtown Dallas," Ishaan told CNBC.
Combined, their energy usage costs them US$3000 per month. That's a lot of glasses of home-made lemonade.
The duo plan to invest their profits back into the business as well as saving some for college fees in the future.