Melvyn Wall, 66, was found guilty of sexual abusing three children between 1993 and 2014.
He was jailed at Leeds Crown Court yesterday after being found guilty of four offences of sexual assault, four of sexual activity with a child, two of indecency and three counts of indecent assault.
Detective Chief Inspector Sue Jenkinson, of Wakefield District Police, said: "Melvyn Wall richly deserves the long sentence he is starting today for a pattern of sexual abuse against young and very vulnerable victims.
"He also put his victim's through the ordeal of a trial, forcing them to relive the harm they suffered.
"I want commend their courage for the way they conducted themselves during the trial process.
"All reports of child abuse are dealt with the utmost sensitivity and police and the CPS will do everything they can to bring those responsible to justice."