The offences occurred between October 2019 and this March, and took place in the Teesside and County Durham areas.
Gut wrenching emotional statements by the parents of the children Slimings abused were read out in court.
One mother said her once happy, innocent child had been left traumatised and too afraid to leave her side.
The parent said: “Children are not safe around him and they never will be.”
Another mother told of the “indescribable pain” when her child revealed the horror of the abuse to her.
And another parent said their child had had their childhood “stolen” from them.
Judge Howard Crowson said Slimings, of Wellington Drive, Wynyard, concealed a “deviant and appalling” sexual interest in children for many years.
Judge Crowson told him: “The harm that you have caused, and which you ask me to believe you now feel remorse about, will last a lifetime.”