A paedophile forced an 11-year-old boy to wear a nappy with a plastic doll inside in order to teach him "where babies come from" before he raped the child.
James Pulman, from Kidderminster, Worcestershire, has been found guilty of sexually abusing four children - even filming himself abusing one of them.
One of his victims was abused for over a decade and Liverpool Crown Court heard how he had raped two of his victims.
The 53-year-old has now begun a 27-year prison sentence after being convicted of three rapes and 15 indecent assault charges, happening on multiple occasions, on one victim.
Pulman, formerly of Liverpool, was also convicted of 12 charges involving two other boys and a girl on Wednesday (23 August) with the judge imposing an extra two years extended licence.
The judge said that he was satisfied that the main victim, who was abused for more than a decade, has "suffered severe psychological harm. The impact on him has been nothing short of life changing".
In a victim impact statement, the boy who was abused the most by Pulman said the paedophile was responsible for "the commotion" in his life, according to Kidderminster Shuttle.
Another victim, abused between the ages of seven and ten, chose to live with his violent alcoholic to get away from Pulman after the pervert had discussed murdering someone with him.
The court hear that another of Pulman's victims was handed £1 aged eight so the paedophile could touch him sexually.
The fourth victim was an 11-year-old girl he indecently assaulted when touched her breasts and tried to put his hand down her pants.
During the trial it was heard that Pulman took a doll out of one victim's nappy and told him that it was where babies came from, reported The Mirror.
Judge Denis Watson, QC, said that he had abused him "in the most grotesque way from the age of five."
"You either targeted or exploited very young children and there was intimidation of these victims preventing any reporting," he told the court.
"It was a sustained course of conduct involving a considerable degree of planning and abuse of trust. You have been convicted of a huge number of criminal offences."
Pulman had maintained his innocence during the trial but will now be ordered to sign the Sex Offenders Register for life. He will also be subject to an indefinite Sexual Harm Prevention Order and a restraining order.