Ian Samson, 72, is starting a 14-year jail sentence for a catalogue of abuse that included a number of attacks on youngsters at the Lord and Lady Polwarth Children's Home in Polwarth, Edinburgh. The home closed in 1982.
Samson gained his job as a janitor at the house despite being suspected of taking obscene photographs of a child at the institution.
He also abused dozens of other children at a boys' hostel, including customers of his ice cream van and children employed in his shop. He also hunted down young victims hanging around the streets.
Samson had been convicted after trial of 22 offences involving the sexual abuse and rape of 12 children. His abuses were spread across the capital, East and West Lothian in the 1980s and 1990s.
One victim was abused by Samson for more than 10 years. The abuse began when she was too young to understand what was going on and escalated to "repeated rapes on an almost daily basis".
Sentencing him at the High Court in Glasgow, Judge Lady Scott told Samson: "You have organised and conducted your whole life to gain access to children and to perpetrate sexual abuse."
She said he was still a serious danger to young children, adding: "You appear to have seized every conceivable opportunity to abuse a child."
Samson has also been put on the Sex Offenders' Register indefinitely.
The Kirk last night announced a critical review of the period when Samson worked at the home. The three person inquiry is to include a representative from Crossreach, the internal division responsible for care homes, its safeguarding team and an individual from outwith the Kirk.
A spokesman said: "There are no adequate words to convey how horrified we are by the abuse these children suffered. Ian Samson's crimes are truly sickening."
The spokesman said the Church would try to see if lessons could be learned. He added there had "at this moment been no contact with any of the survivors of the case".
He would not comment on why such a review had not been set up before Samson's sentencing.
Allegations of abuse first surfaced in 1991. This was when a woman also reported the abuse but she told Samson's trial she was not believed.
Lady Scott commented: "Such circumstances may be a reflection of the fact this conduct was historic and standards and understanding have undoubtedly changed. Nonetheless, there may have been a failure of protection here that ought to be reflected upon by all the agencies involved."
The judge told Samson: "The offences of which you have been convicted reflect a wicked campaign or course of conduct persistently pursued to abuse children over a period of years.
"The sheer length of this course of conduct, over 30 years, is an important factor in determining the appropriate sentence here.
"You held a position of trust over many of your young victims as their surrogate 'dad' or uncle; or as their employer."
Police said Samson was charged in connection with these offences after officers carried out inquiries into his background following his conviction in 2010 for similar cases of abuse. They found he worked at a care home in the 1970s and traced a number of his victims.
Detective Chief Inspector Kenny Gray said: "Ian Samson is a manipulative and cunning individual who, over three decades, abused children.
"He presented himself as a respectable member of the community. However, he preyed on children whose lives were made a misery as a result of his sickening behaviour."
l Police Scotland's investigation into abuse allegations at the Catholic Fort Augustus Abbey, in the Highlands, and Carlekemp School, East Lothian, has already identified more than 20 possible victims.