Wayne Traill, 52, of Stonebridge Road, Northfleet, carried out his crimes over more than a decade and targeted three children.
One victim was abused in the 1990s, while two others were exploited later.
He warned them they would not be believed if they told anyone.
Police became involved in March 2022 after the abuse was reported.
Traill was arrested but refused to cooperate during interviews.
He initially denied all charges when the case went to court.
Just before his trial at Woolwich Crown Court, Traill pleaded guilty to 21 offences, including rape, attempted rape, sexual assaults, and gross indecency.
On December 19, 2024, he was sentenced to 21 years in prison.
Upon his eventual release from prison Traill will be the subject to an extended licence period of eight years.
He will also remain on the sex offenders register indefinitely.
Detective Constable Daniel Grant of Kent Police said: “Traill repeatedly subjected his victims to depraved and sickening abuse, causing incalculable damage upon their young lives.
“He is a predatory child sex offender who used fear and intimidation to obtain sexual gratification, and whose deplorable actions will sadly have a lasting and profound impact on those he targeted.
“The fact justice has finally been served is largely down to the incredible courage and bravery of his victims and I’m grateful Traill is at least now behind bars where he can cause no further harm to other young children.”