“The effect on them was horrific.
“What you did to them was truly monstrous, I can’t describe it better than they did in their victim personal statements but I have to agree with their descriptions of you.”
Probation officials said Cairns offending was for “sexual power, control and sexual attraction to children”.
Judge Spragg told him: “You have been an extremely dangerous man throughout your life.
“You must never be left alone with a child.”
Cairns must sign the sex offenders register and abide by a sexual harm prevention order for life.
He was given an extra one year extended licence period on top of the 28 year sentence, of which he will serve at least two thirds.