Frederick Savage, 64, repeatedly abused a girl and a boy while he was living in Halifax, in the 1980s.
He then vanished from the area after splitting up with his partner but his male victim, now aged 30, made contact with him through the social networking site in 2010. His first message got no reply but the victim - who was abused at the age of eight - saw Savage online on the site's chat facility and sent him a message telling him of the heartache he had caused.
Savage, by then living in West Sussex, replied and later confessed to his wife, who called the police.
Bradford Crown Court was told on Thursday that the girl, now 32, was abused from the age of four until she was nine.
Both she and the boy were made to perform sex acts with Savage.
Savage, who was jailed for three-and-a-half years, admitted two counts of gross indecency with children and three of indecent assault.
Judge Jonathan Rose said: "These were depraved and wicked offences against defenceless children.
"There's no reason for any person to act in this way to a child. I am entirely sure you did so only for your sexual gratification.
There's no excuse or justification for such abhorrent behaviour."
The court was read a pre-sentence report in which Savage claimed the children had instigated the offences.
The probation officer believed he still posed a serious threat to children.
Savage was given 21 month consecutive sentences for his offences against each victim and a lifetime sexual offences prevention order was put in place.
The court also heard that in 2005 Savage and his wife had been carers for a local authority and had looked after two teenagers.