Robert Foulkes, 65, pled guilty to three charges at the High Court in Edinburgh on 13 September 2024.
The retired health and safety officer repeatedly targeted the victims in the Aberdeenshire area over a 12-year period.
During the campaign of abuse, Foulkes used a mobile phone to film himself abusing one girl before showing her the footage.
He also admitted causing two of the children to watch pornography before sexually abusing them.
Foulkes told one victim that his abuse was “their little secret”.
On 22 October 2024, at the High Court in Edinburgh, Foulkes was given an 18-year extended sentence with 15 years in custody.
His name has been added to the sex offenders register indefinitely.
Non-harassment orders, preventing Foulkes from contacting or attempting to contact the victims, were granted for an indefinite period.
Scotland’s Procurator Fiscal for High Court Sexual Offending, Katrina Parkes, said: “Robert Foulkes posed a significant danger to children through his predatory behaviour.
“The trauma suffered by the victims was at the forefront of our minds during this prosecution.
“It is thanks to the bravery of those affected by Foulkes and his offending that he has now been brought to justice.
“We would encourage anyone affected by similar offending to come forward - regardless of how much time has passed.
“You will be listened to and supported as we seek to secure justice using all the tools at our disposal.”