"The bottom line for the two of you is that I'm sure you both pose a very high risk of serious harm to others."
Referring to the victims' families, he said: "I want them to know that I've taken into account the devastating effect that all of this has had on their lives and the lives of their boys.
"I have no doubt that they would have preferred to see [the two brothers] locked up for very much longer and I know that nothing can compare to the trauma the boys went through, but I hope they appreciate that five years is the very least they will serve."
After sentencing, Doncaster Council offered a profuse apology to the victims for deficiencies which left the brothers free to attack.
Director of children's services Nick Jarman offered "an unqualified apology" for the failings "which led to this terrible incident".
He said an independent investigating officer would be appointed and where serving or former staff were found to be culpable disciplinary action would follow.
Clive Coleman, legal affairs analyst
Indeterminate sentences consist of a minimum period of custody, known as the tariff, which the prisoner must serve.
Once the tariff is served, the prisoner will not be released unless he or she can satisfy the authorities that they no longer pose a threat to the community.
That means that prisoners can remain in custody indefinitely and it is for that reason that some have criticised indeterminate sentences as the new 'life' sentences.
Prior to their introduction the authorities were powerless to stop some criminals who clearly remained a danger, but had served their sentence, from being released.
In a statement issued through police, the boys' families said the events had "rocked our lives".
"We have found the last nine months to have been an extremely difficult and testing time," they said.
"Hearing the evidence in court during these past three days has also been deeply upsetting for us all."
Describing the effect of the attack on the victims, the judge said: "Their physical and emotional scars will live with them for a long time to come.
"Their relationship with each other has been seriously affected and their parents have been left with a strong sense of guilt, which they didn't begin to deserve, about whether they could have done more to protect their boys."
Part of the attack was filmed by one of the brothers on a mobile phone.
'Domination and degradation'
The judge said: "By recording parts of what you did on a mobile, you made at least some of this an example of happy slapping."
The judge said the boys had chosen their victims because of their vulnerability.
He told the elder brother: "You wanted to assert your dominance over them by the use of aggression, extreme violence and sexual degradation and inflicting pain in order to gain a sense of power and control over their lives."
Sgt Richard Vernon: 'It's the worst thing I've seen in 22 years'
The judge said the younger boy had controlled the victims by "domination, degradation and inflicting pain for the purpose of your own emotional pleasure."
The brothers showed no emotion as the sentences were passed. As they were led out of court the mother of their younger victim swore at them and called them "evil".
The elder brother told police he attacked the boys because he had been bored and "there were nowt to do".
The court earlier heard the brothers, who were placed in foster care a few months before the attack, had a chaotic upbringing with their violent father, mother and five brothers.
They were shown "extreme" horror films and the younger brother had access to pornographic DVDs and smoked cannabis grown on his father's allotment.
Speaking about the case, Det Supt Mick Mason of South Yorkshire Police said: "This is clearly the most traumatic investigation I have ever come across. Not the most difficult - but the most traumatic."
The court was told how the boys were approached by the brothers on 4 April and lured to an isolated wood ravine where they were strangled, stripped and forced to sexually abuse each other.
The elder victim was seriously injured when pieces of ceramic sink were dropped on his head.
After their tormentors left the scene the injured boy told the younger victim: "You go and I'll just die here."
The blood-soaked boy raised the alarm and the elder boy was later found lying face down with the bottom half of his body naked.
One of the men who found him told the court he feared the youngster had died.
The attackers were placed on the sex offenders register for three years.
The boys also received 24 months' detention for the offences of causing a child to engage in sexual activity and 18 months' detention for robbing the boys.
They were each sentenced to 30 months' detention after they admitted causing another 11-year-old actual bodily harm a week before the young boys were attacked.
All sentences will run concurrently.
Following sentencing a hearing was held in which the judge ruled he would not lift restrictions banning the reporting of the defendants' identities.
A BBC investigation has revealed the two attackers were well-known troublemakers and social services were heavily involved in their lives.
A Safeguarding Children Board report, seen by BBC Newsnight, found the attack could have been prevented.
Chair of the board, Roger Thompson, said: "No-one could have predicted the severity of the attack. However, the review has concluded there were serious failings in local services."
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