World Vision says children in southern Africa are being forced to sell their bodies to buy food for their families, who have been hit hard by extreme drought.
They're blaming climate change for the record dry conditions, which have destroyed crops and the livelihoods of millions of people.
World Vision spokesperson Maria Carolina expects the number of people in poverty to rise dramatically.
"Eleven million people are affected by drought and hunger in southern Africa, and we expect this number to rise up to 45 million," she said.
Rising temperatures and poor rainfall have meant parts of southern Africa are now suffering from the worst drought in living memory.
Crops are dying, and food shortages have forced children to pick up the pieces.
"We've spoken to many of them that had to walk long distances to access water, they have to skip school, or even girls that are selling themselves to bring food for their homes," Carolina said.
Cavo, 15, is from Angola and says prostitution is the only way her family can survive.
"I do this because of my mother. She is suffering because of hunger."
She says the men she's often forced to sleep with give her as little as 40 cents.
If it weren't for the drought, Cavo would be studying.
"If men come, then I sleep with them. If I deny them, how will I survive?"
Zimbabwe has also been hit hard and people have suffered at both ends of the weather scale - first by devastating floods, and now from dry conditions.
Temperatures have risen by more than two degrees in the past century, and maize production has reduced by 54 percent over the past year.
Local farmer Talkmore Whishiki said due to the shortage of water, he isn't getting enough to support his family.
"We are struggling and struggling."
World Vision is now working to raise $65 million to help the children in southern Africa.
A Zimbabwe youth leader is calling on world leaders to pay attention to the climate crisis.
"The leaders should at least listen to us. When they make decisions, they should also include us," Melody said.
Without the countries' leaders addressing climate change, children like Cavo will continue to be forced to make choices no child should have to make.