Chilling accounts by former child fighters, some of whom enlisted as young as seven, were released on Thursday in a 150-page report by Human Rights Watch entitled, "You'll Learn Not to Cry: Child Combatants in Colombia."
"They'd kill three or four people each day in the (training) course," said Oscar, a former paramilitary fighter recruited as a boy. He described watching prisoners mutilated with knives or chainsaws, as part of his "conditioning."
"Different squads would take turns, would have to do it in different ways," he added. The paramilitary death squads kill rebels and suspected guerrilla sympathizers.
The rights group estimated there were at least 11,000 children fighting in Colombia's four-decade-old conflict, which claims thousands of lives every year.
Former Marxist rebels described attending torture sessions of prisoners, needles pushed under finger-nails, digits severed, arms cut off, and faces disfigured.
Underage female guerrillas said they had sometimes been pressured to have sex with older commanders.
"Their commanders used their power to have sexual relations with many underage girls, required them to use contraceptives when they were as young as 12," said Jose Miguel Vivanco, executive director of the group's Americas Division.
Outlawed armies from the far-right and left both threaten deserters with execution, and often force child fighters to carry out the death sentences. Elizabeth, a former fighter with the Revolutionary Armed Forces of Colombia, or FARC, recalled voting against an execution sentenced by the war council.
"They told me to shoot again ... In the night, I couldn't sleep I was so scared. I sensed that he was standing at my feet"
Former FARC child fighter
"There had been a war council and I had voted no. The commander told me, 'Since you voted no, you will be the one to kill him,'" she said.
Another former FARC fighter described killing an army sergeant sentenced to death. He was 12 years old.
"My first shot missed because I was so scared and my hand was trembling so much I couldn't keep the revolver still. Another guy grabbed my hand to steady it ... With the second shot, I hit him in the leg and he fell over," the boy, named Ramon, was quoted as saying.
"They told me to shoot again. The next shot hit him in the chest and another one here. In the night, I couldn't sleep I was so scared. I sensed that he was standing at my feet."
Most Colombians live in poverty, providing an enormous pool of recruits for outlawed armies on the far-left or right. Eighty percent of the children under arms in Colombia belong to one of two guerrilla groups, the Revolutionary Armed Forces of Colombia (FARC) or the National Liberation Army (ELN), said Vivanco.
In a particularly dark chapter of the report, "Paid Killers: Child Paramilitaries," former gunmen describe getting "bonuses" for brutal assassinations.
"He was the chief of police in my town ... They showed me who he was and gave me three days. I called him as if to seduce him," said Laidy, who joined the paramilitaries when she was fourteen.
"I was with another paramilitary girl of fourteen. We took a paramilitary taxi - many taxi-drivers support us. The man said, 'Why are you going to kill me?' I told him that he had problems with us. I shot him in the head with a .38 revolver. It wasn't hard for me because I had already been in combat."