Matthew went to Afghanistan to report on the situation for Newsround Extra, where he met 12-year-old Gholshah, who lives in a village called Kharistan.
Her family have nothing left to sell, so her father has engaged her to be married - in return for £60.
Golshah told Matthew she understands there's no option: "I didn't say anything to my dad because my sisters were hungry."
Never happened so young before
It is a tradition in Afghanistan - and many other countries - that families get some kind of payment for their daughters, called a dowry.
But this would normally happen at 18.
It's never happened at such a young age, and certainly not to get food to survive.
However Gholshah understands that she's doing this because there seems to be no other option.
"My brother and sister were hungry - we didn't have any choice that's why they gave me away to marriage", she says.
"We were desperate - we had no choice my sister was fainting from hunger."