A report has said the attack on the two boys could have been prevented
Two brothers threatened to kill two boys in a brutal ordeal in which the victims were stamped on and attacked with broken glass, bricks and sticks.
Sheffield Crown Court heard the pair, aged 10 and 12, led the youngsters to an isolated spot in Edlington.
One victim was forced to strip naked and perform a sex act and a metal ring was used to strangle one boy, the three-day sentencing hearing was told.
The pair have admitted causing grievous bodily harm with intent.
They have also each pleaded guilty to robbing one of the boys of a mobile phone and the other of cash and have admitted two counts of intentionally causing a child to engage in sexual activity.
They are being sentenced in a hearing that is expected to last three days.
Child protection expert Dr Eileen Vizard told the sentencing judge, Mr Justice Keith, that the younger brother was a "very high risk" to the community and was at risk of becoming "a seriously disturbed psychopathic offender" unless he was properly treated.
She said he demonstrated "callous, unemotional traits" and "showed very little, hardly any empathy for his victims".
The judge was told the victims, then aged nine and 11, set out on Saturday 4 April with their BMX bikes and their dog.
They were approached by the brothers after they went to a shop and the brothers, whom they had met before, asked to use their bikes.
They then asked their victims if they wanted to go and see a dead fox.
Prosecuting, Nicholas Campbell QC said the brothers took hold of their victims and dragged them through a gap in a fence, while threatening to kill them.
During the attack, the older brother focused his attention on the older victim, while the other brother targeted the younger boy.
The prosecutor said the victims, who are uncle and nephew, were subjected to an assault that was "both physically painful and emotionally traumatic - it was frightening".
"In addition, what they endured was humiliating and embarrassing."
The court was told the brothers stamped on their victims and collected bricks and stones, which were thrown at their heads.
The two attackers were arrested by allotments in Edlington
Police who searched the scene later found a great deal of blood and blood-stained "weapons" including a wooden branch and a stone weighing 28lbs.
The court heard how a metal ring was used by the elder brother to attempt to strangle one of the boys.
Mr Campbell said one of the boys was stripped naked and was told to perform a sex act.
When people were heard approaching the area, a plastic sheet was placed over the two boys, which was then set on fire causing burns to the boys.
Mr Campbell said when the younger boy refused to cross a stream he was told: "If you're not going to come over here, then you'd better kill yourself. Otherwise we're going to come over and do it."
Eventually the younger defendant said they had to go to meet their father.
Mr Campbell said: "[The older brother] replied 'One minute. I need to kill them both because they might just grass on us'."
Rocks were then thrown at the two victims before the pair left, telling the two boys to stay where they were or they would "come back and finish you off".
The families of the two victims gasped and cried as mobile phone footage of part of the attack was played in court.
The 20-second video, taken by one of the brothers, showed his sibling taunting and hitting one of his victims as he lay on the ground covered in blood.
The brothers have also admitted causing another 11-year-old boy actual bodily harm a week before the young boys were attacked.
A BBC investigation has already revealed the two attackers were well-known troublemakers and that social services were heavily involved in their lives.
A Safeguarding Children Board report, seen by BBC Newsnight, found the attack could have been prevented.