Mr. Karzai called them “innocent children incited by the enemies of Afghanistan.”
One of them, Nasibullah, who was said to be 10 at the time, although he looked much younger, was rearrested less than a year later. The National Directorate for Security, the Afghan intelligence agency, said he was preparing a second suicide attack using a vest of explosives.
At a news conference after his arrest, Nasibullah again expressed contrition and begged for his release, promising not to return to the madrasa where he had twice been trained.
Nearly all of the boys arrested on charges related to suicide attacks were educated in madrasas, conservative religious schools that can serve as recruiting and indoctrination centers for suicide bombers.
Nasibullah was not released at the time, but despite still being a minor, he is no longer in the juvenile detention center. Justice Ministry officials said they did not know what had happened to him.
Mr. Anwar, the justice minister, said that sentences for child offenders were often lenient because of their ages, but that the ministry lacked funding and facilities to provide them with counseling and support to steer them away from extremism.
“The majority of them when they’re released go back to fighting against the government,” he said.
The Afghan intelligence agency had proposed that would-be suicide attackers be held indefinitely after completing their sentences because of the risk they posed to society, Mr. Anwar said. “The courts said no.”
Like his fellow prisoner Muslim, Atiqullah, the 16-year-old whose bomb went off prematurely, also chanted a Pashto poem he had learned while in prison, an elegy both lamenting and praising imprisonment. He squatted and sang for his visitors in a youthful tenor:
In our chains there are lessons to be learned.
The sun shines and reveals the secrets of our world.
The chains are beautiful, creations of God:
The chains on our hands hurt us,
But the scars on our hands teach us.