A teenager exploited the failures of a mum as he raped and sexually abused two of her vulnerable children.
Brandon Mullin preyed on the youngsters, siblings a judge said were victims of the worst neglect he had ever seen.
His terrible abuse only ended when the children were taken into care.
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Mullin, now 19, was convicted of 10 sexual offences against two victims following a trial at Liverpool Crown Court.
His crimes included the rape of a boy and abuse of a girl.
Mullin was a child himself at the time of the offences, though Judge Garrett Byrne today declared: "I am satisfied you knew perfectly well what you were doing was wrong."
Passing sentence on Monday morning, Judge Byrne described Mullin as a "cold and calculated individual" who had no regard for the impact of his actions on his victims and had displayed no remorse for his "wicked deeds".
He added: "The harm you have caused these children is incalculable. You have caused them physical, emotional and developmental harm. The harm will last the rest of their lives."
Classing Mullin as a dangerous offender, Judge Byrne handed the teen 13 years' detention at a young offender institution with an extended licence of three years.
This means Mullin will be locked up for at least two thirds of his detention period before he can be considered for parole.
Once released, he will be subject to strict conditions for the rest of that 13 year sentence, plus a further three years.
He was also given a lifetime sexual harm prevention order.
Ian Whitehurst, defending, had told the court Mullin was found to have been a "vulnerable and immature individual" at the time of his crimes and that "there was no structure in his life whatsoever".
He said there had been a "marked improvement" in his client since he had been taken into custody and that he was now engaging with a number of rehabilitation services behind bars.
The court had previously heard of the backdrop that allowed Mullin to prey on his victims.
The children, and their other brothers and sisters, grew up in a chaotic and filthy environment without adequate food and clothing, basic hygiene, medical care, any toys or love.
Judge Byrne said their home had not been safe with many people - mostly "strangers" to them - coming and going.
Their mum, who cannot be named because that would identify her children, admitted five counts of neglect relating to each child "from birth until the date of their removal by social services".
Her pleas were made on the basis she did not know about the sexual abuse and was not involved in it.
This was accepted by the Crown Prosecution Service.
Sentencing her last month, Judge Byrne said while the mum didn't "participate" in the abuse, her neglect "led" to it.
He told her: "You were rarely there, choosing instead to prioritise your own needs over those of the children."
He added that her neglect meant Mullin " was afforded the opportunity of sexually abusing them ".
The judge said: "If your basis of plea is you had no responsibility for that, then I reject it.
"I accept you didn't know about the abuse. But if you exercised greater control... that abuse may not have occurred."
David Polglase, who prosecuted both the mum and Mullin, said agencies and professionals had tried to support her.
However, he said a family support worker noted she was "clever" in "giving out the right signals but then not complying", while the judge observed she would "pay lip service but fail to follow through with action".
The court heard a turning point came when one of her children, a little boy, was found " wandering the street, barefoot, with no coat, in cold weather, in wet clothes and with a wet nappy".
The mum, who also admitted possessing drugs with intent to supply in relation to a police swoop after her children had been removed from her care, was sentenced to 12 years in jail.
Speaking as he locked up Mullin, of Kensington Road, Kensington, Judge Byrne said the only positive to emerge from the case was that the children were now being looked after by loving, caring foster parents.
Adults concerned about a child can contact the NSPCC helpline, seven days a week, on 0808 800 5000, or email help@nspcc.org.uk.
Anyone with information about a sexual offence allegation can call police on 101, where you will be spoken to by specially trained officers, or you can pass information to Crimestoppers, anonymously, on 0800 555 111.
Support for victims is also available from the registered charity the Rape and Sexual Abuse Support Centre Cheshire and Merseyside, who can be contacted on 01925 221 546 or 0330 363 0063, or Rape and Sexual Assault Merseyside (RASA) on 0151 558 1801.
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