Ishaan Thakur, 14, and his sister Aanya, 9, have seen their college fund swell this year after they began mining in March with an old gaming computer.

That first month, they made $1,000, reports the Dallas Morning News. The numbers have soared since then.

With interest spurred after hearing their father talk about the rise of cryptocurrencies, the pair initially wanted to invest in crypto, but it was already too expensive, so with the help of YouTube and their father, the ninth-grader and fourth-grader learned how to mine. They’ve reinvested their earnings to buy additional equipment, signing up for supply updates (generally graphics cards) from nearby electronics stores to fight this summer’s chip shortage.

They currently have 94 processors mining—making about 9 billion guesses per second at codes. When they get it right, they’re rewarded with crypto.

Their business, which they named Flifer Technologies, was initially housed in their garage, but as it has grown, they moved most of their rigs to an air-conditioned data center in downtown Dallas. They keep 30 cards in the garage setup, however.

Between the two locations, they spend about $2,500 a month on energy bills. While they’ve sold some Ethereum to cover expenses like the hardware, power bill, and rent at the data center, they’re hanging onto the majority of it, hoping it continues to grow in value.

Ethereum has been on a tear this year, increasing in value by 334% since the start of the year, according to CoinDesk.

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