When they do sit still for a rare moment of reflection, they tell of fathers killed by the Taliban or in Nato air raids, legs blown off by discarded rockets and families torn apart by war.
In contrast to their grim stories, the boys appear to embrace life surrounded by friends their own age, sleeping 16 to a dormitory and rising before dawn to start a daily routine of prayers, classes and raucous kick-about games.
"We get up at 4.30am to pray, then breakfast, then lessons and playing all day," said Hamidullah, 17, who has been at the orphanage outside Kandahar city for two years.
"We have a rest after lunch and in the evenings we chat, read or do extra work. The teaching is very tough to help us get good exam results. We do all subjects – maths, Pashto, English, religious studies and computers."
Afghan orphans play football in the yard of the Shiekh Zayed orphanage in Kandahar. (AFP Photo)
Hamidullah says his uncle brought him to the orphanage after his father was killed in Ghazni province by a Taliban roadside bomb.
"My father was a police commander and there was an IED (improvised explosive device) on the way that he was travelling. It exploded and killed him," he said calmly.
Many Afghan families are so poor that when a father dies, widows are unable to care for sons who instead end up working, begging or are taken one of the country's few orphanages.
"I telephone my family once a week to speak to my three sisters and brother," Hamidullah said. "I miss them, but the life here is good."
A packed timetable of lessons and football keeps boys at the Shiekh Zayed orphanage in southern Afghanistan occupied every minute of the day – one way to deter them from dwelling on the tragedies that brought them there. (AFP Photo)
'The best day is Friday when we go on a picnic'
The all-boys orphanage, funded by the UAE royal family, runs a demanding regime with students encouraged to aspire to successful careers despite their troubled backgrounds.
There is no television or Internet, and entertainment is restricted to the occasional film shown on a projector.
Classrooms are full to bursting with pupils squashed onto wooden benches, and teachers expect complete attention from the boys. Poor results can mean being thrown out of the orphanage.
"I want to be a doctor," said Mujahid, 13. "We do get given a lot of work, but the best day is Friday when we go on a picnic or to the bazaar."
An Afghan orphan sits on his bed while studying at the Shiekh Zayed orphanage in Kandahar. (AFP Photo)
Mujahid's father was killed outside their home in Uruzgan province by a NATO air bombardment four years ago.
"He was working in the fields during the day when he was killed," he said, reluctant to recall more details of that day. "I go home for holidays in the summer."
Among the most ambitious students is Sayad Wali, 14, who walks on two artificial legs.
He wants to work in television or radio, and admits with a grin to loving Afghan pop music despite the teachers' stern disapproval.
"I was feeding animals in my village when someone was carrying a RPG (rocket propelled grenade) out of a mosque where it had been left," Wali, from volatile Zhari district in Kandahar province, said.
"The man bumped the rocket on a tree and it exploded. My nephew died and I was taken by ISAF (the NATO force) to their Kandahar hospital for treatment."
Wali, whose father died of natural causes, lost both his lower legs and one knee, but he walks well despite suffering bad skin abrasions during the summer heat.
Now he wants to press ahead with his lessons.
"I hope to go to university and do television work one day," he said.
About 220 orphans, aged between seven and 20, board full-time at the school, with other orphans and local boys pouring in by the day for the two shifts of lessons.
An Afghan teacher writes on a whiteboard as he teaches English to orphans at the Shiekh Zayed orphanage in Kandahar. (AFP Photo)
All wear white skull caps and plain shalwar kameez robes – brown for the morning shift and blue for the afternoon.
Lunch of rice, meat and dal is served from huge steel pots to noisy queues of pupils carrying steel trays, and afterwards desert is a single apple.
"We are full beyond capacity," said director Mohammed Shafiq. "There are only a few other small orphanages around, and we have to turn many candidates away."
"The boys we look after often come from sad families, so we try to provide a happier environment."
"We want to teach them to be an example to society, to show that education is something to care about, and to help them develop into complete human beings."
The bitter world of revenge killings, blood feuds and insurgent warfare in the Pashtun heartlands of Afghanistan is kept safely outside the orphanage's gates.
But Shafiq knows his pupils face many difficulties and dangerous temptations once they leave – including the risk of recruitment by the Taliban.
Even with the education the orphanage provides, the future for the boys is not certain. Some go on to university, become teachers or take low-level government jobs, but many others struggle to find regular work.
"We have a responsibility to teach them and guide them," Shafiq said. "Afterwards they must choose how to live their lives."