These girls' 13-year-old sister was sold to buy food (Photo: Sam Barratt, Oxfam)
Tens of thousands of people face starvation this winter in western Afghanistan - despite a huge international aid effort.
About seven million people depend on aid in Afghanistan - but the disruption to supplies during last year's fighting broke a vulnerable food chain.
Tuberculosis is spreading among people weakened by hunger.
The worst affected area is the mountainous province of Badghis, in western Afghanistan.
Half of the houses in the remote mountain village of Siah Sangh are empty.
Some villagers have taken refuge in squalid camps around the nearby city of Herat.
Other have died of hunger or related diseases.
Aid vehicles carrying food and medicine plough through mud and dirt tracks, trying to reach villages like Siah Sangh.
Lack of doctors
But when we get to the end of the road, all we can do is walk - as do most people who live in these inaccessible areas.
Our guide is a boy aged only 13 or 14, who carries a Kalashnikov rifle.
He has spent the morning walking to the village, carrying medicine for his brother.
He doesn't know what his brother is suffering from - but the medicine he is carrying is for tuberculosis.
There is no doctor in his village, but he says he's lucky to live only a few hours' walk from the clinic.
Asked why he carries a gun, he replies that it is for hunting, to shoot a bird that might be food for his family.
Graves
Climbing up a narrow canyon, we reach a graveyard on the hill above that seems to dwarf the village.
We find a woman praying beside the grave of the one-year-old baby she lost this winter.
"My child died of hunger. He was pale and weak, he could not move and he died because we did not have anything to give him."
Until last summer, there were still a few sheep and cattle in Siah Sangh.
But now the last animals have been sold, and families have resorted to selling their own daughters for grain.
Food as money
The dowry system has always given girls a value, but it is the first time that seven-year-olds have been sold off for a few sacks of wheat, villagers say.
Grain is the new currency in the mountains.
Much of the food which has come in this weekend has gone straight to "grain lenders" in the bazaar.
Last year they gave villagers food as credit.
Now the villagers have to repay their creditors before they can eat themselves.
An Oxfam aid worker explains the system:
"When we are distributing the food a very big part of this food is going back to pay the shopkeepers," he says.
"Even if they are hungry they have to pay their debts back to the shop keepers."
The only answer for Oxfam is to pump in more food to fill the backlog.
They lost three months during the fighting and in that vacuum people died.
Informal camps have developed around grain distribution points because many people are too weak to carry their food home.
As a desperate last resort, some have turned to eating a sort of clover which grows in the grass and barren fields - where wheat, barley and watermelons were once cultivated.