"Thank you for what you and your friends are doing to help children in Yemen," the Hollywood star wrote in a signed note to Ayaan Moosa and Mikaeel Ishaaq, both six. "I'm sorry I'm not able to buy a lemonade from you, but I'd still like to make a donation to your stand."
Helped by their parents, the pair set up their sweet-hearted and sour-tasting venture on the street where they live in east London around a month ago. Together they serve freshly-squeezed lemonade for £2 ($3) to passers-by.
"They have nothing, like, the things you need to survive. They have no water, food, oil. And we have all of those things and that's why we help them," Moosa told NBC News about Yemen, the Arab world’s poorest nation, which has been convulsed by civil war since 2014.
That is when the Iranian-backed Houthis took control of the country’s north, including the capital of Sanaa. The Saudi-led military coalition intervened against the Houthis the following year, conducting relentless airstrikes and a blockade of Yemen.
More than 100,000 people have died since then and millions more are suffering from food and medical shortages in what the United Nations has called the world's largest humanitarian crisis. Past attempts at ending the conflict have stalled.
Jolie was appointed a U.N. Special Envoy in 2012, focusing on global crises that result in mass population displacements. The actress has visited multiple refugee camps across the Middle East and has often used her fame to cast a spotlight on humanitarian issues.
A spokesperson for Jolie could not be reached for comment about the donation.
While the boys admitted they had not heard of the "Tomb Raider" and "Maleficent" star, they said their fathers had.
"When our dads were telling us about her, they said she was really pretty, really good actress, really nice person, and then we knew who she was," Moosa said.
The paper note from the Academy Award winner which was posted to their home, is now printed, framed and stands proudly at the front of their stall. The family did not disclose how much the star donated or how she gave them the money, but said it was a substantial amount.
"This is beyond our wildest dreams," Moosa's mother Adeela said.
"To get the recognition of somebody who genuinely cares, that really meant a lot to us," added his father Shakil, 37.
They said the lemonade stand idea was born over the summer after the parents showed the boys videos of Yemen, to teach them about charity, compassion and educate them on how fortunate they are.
"It's really helped them understand and appreciate what they have," Adeela said.
Ishaaq and Moosa said they used a secret recipe for their drink.
Although they have not spoken directly to Jolie, they did record a thank you message to her on Instagram, inviting her to stop-by for a fresh glass of lemonade next time she's in London.