Richard Cade was under a life-time sexual offences prevention order which prevented him from entering any residential property where any person under 18 was living.
But after serving a sentence imposed in London he moved back north to live in his former home town of Gainsborough.
Richard Sheldon, prosecuting, told Lincoln Crown Court that a woman who knew Cade from their school days in the town got in contact with him not realising of his past.
Cade then became friendly with the woman and her partner and got to know their children.
Mr Sheldon said Cade became so trusted that he was allowed to walk with the children into Gainsborough town centre.
He told the court that the woman was unaware of the ban on Cade having contact with children.
He said: “She had been told by the defendant that he had been to prison but he said that it was for theft.
“Matters came to light in June when she was sent a Facebook page that identified the defendant as a paedophile.
“She confronted him and he claimed he was wrongly convicted.
“He was told not to visit again and not to contact the children.”
Mr Sheldon said that inquiries had not revealed anything untoward happening between Cade and the children.
Cade, 30, of Trent Street, Gainsborough, admitted breach of a sex offences prevention order on dates between September 1, 2015 and May 31, 2016.
The court was told that he was jailed for two years with a four year licence extension at Wood Green Crown Court, North London, in March 2007 for three offences of sexual assault on a child under 13.
The lifetime sexual offences order was imposed on him on his release from his prison sentence.
Judge Michael Heath, passing sentence, told him: “For a significant period of time you showed a blatant disregard for this order.
“These orders are not made for fun. They are there to be obeyed to protect children.”