A convicted paedophile has admitted abusing 20 children while working as a live-in au pair.
Aaron McWilliams abused children and babies he was employed to look after while staying in family homes across the UK and Europe.
The 28-year-old was sentenced to life for his horrific crimes, which were described by police as 'every family's worst nightmare.'
McWilliams, who is already serving time in Belmarsh Prison for child abuse, was told he will serve a minimum of nine years in jail at Woolwich Crown Court today.
The predator made videos of himself sexually abusing children aged between four months and 14, and detectives now fear there may be further victims yet to come forward.
Police said McWilliams was 'manipulative, cold, calculating, and highly dangerous to children and young people.'
Aaron McWilliams admitted abusing 20 children while working as a live-in au pair
McWilliams was first convicted in 2016 for sexually assaulting a four-year-old child.
After serving part of his sentence, McWilliams was released and began working with a family within a matter of weeks after providing fake references.
He sexually abused another four-year-old child and was jailed again for seven years in August 2017.
During the investigation, a phone was seized and detectives found 2,472 indecent images of children plus an extensive collection of videos McWilliams had made of himself sexually abusing his young victims.
The prolific child predator was interviewed twice in 2018 about the material on his phone and made admissions about his horrific actions.
Some 24 victims, aged between four months and 14-years-old, were identified during the investigation of which all but one were boys.
McWilliams admitted a string of 40 sex crimes against children including 14 counts of inciting a boy under 13 to engage in sex, eight counts of inciting a boy under 13 to engage in other sexual activity and seven counts of sexual assault on a boy.
These also include three counts of making an indecent photo of a child, three counts of sexual assault on a child, two counts of rape of a boy under 13, attempted rape of a boy under 13, sexual assault on a girl and engaging in sexual activity with a boy under 15.
DS Adam Ghaboos, of the Met Police Central East Safeguarding team, said: 'McWilliams is a predatory paedophile who sexually abused a large number of children he was entrusted to care for.
'It is every family's worst nightmare. He is manipulative, cold, calculating, and highly dangerous to children and young people.
McWilliams admitted a string of 40 sex crimes against children at Woolwich Crown Court
'This case is among the most serious child abuse offending that the team has seen.
'I would like to acknowledge the courage of the young victims and their families who have endured the horrific abuse and the long-term harm these types of crimes cause.
'McWilliams will spend a long time in jail where he cannot harm any other children.'
DS Ghaboos said there may be further victims yet to come forward and asked families who have employed McWilliams in the past to come forward.
He added: 'Our enquiries have led us to a large number of McWilliams' victims, but we can't rule out the possibility that there may be more.
'I would urge any families who have employed McWilliams or believe that he may have had contact with their children to come forward.'