Tristan McGowan, 20, pleaded guilty to three sexual assaults on a boy under the age of 13 at Newcastle Crown Court.
McGowan, of Dock Street, South Shields, was handed a 15-month prison sentence for his crimes, suspended for 24 months.
He was also made the subject of a sexual harm prevention order for five years.
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He had initially pleaded not guilty to the charges against him.
The victim’s father told the Gazette of his family’s anger at what they feel is a lenient sentence given to McGowan.
The boy was just six-years-old when he was abused by McGowan, who was then in his early teens, after they had struck up a friendship.
The father said the boy only realised the extend of the abuse he was subjected to when he began having sexual education classes at school.
He said: “We have gone through a horrible few months and this has put a massive strain on us as a family,”
“We feel so let down that he was only given a 15-month sentence and that was suspended.
“We believe that this is simply not enough.”
He added: “What kind of message is that putting out there? People who do these kind of things should go to prison?
“From a family point of view, everyone is shocked at the outcome.
“We all expected a custodial sentence when he changed his plea at the 11th hour.”
The man says his son continues to be affected by his ordeal and finds home and school life difficult.
He said: “My son can’t make friends and he’s finding everything really difficult.
“In his victim personal statement, which was read out in court, he was asked what words would he want to say to Tristan for what he has done to him, and he said ‘thank you for ruining my life’.
“We just hope in time and with the right support that he can get back on track and live a normal life.
“Since all of this came out it’s like he has become a different boy.”