A convicted child sex offender who pleaded guilty to sexually assaulting a teenager at his milk bar has lashed out at his victim, accusing him of lying and stealing money from his shop.

As Fairfax Media revealed on Friday, Brett Barrett, sentenced on Thursday to seven months' jail for three counts of committing an indecent act against the teenager, was able to set up his business just metres from a high school, despite  prior interstate child-sex offences.

The crimes, committed in the 1990s, predate the National Child Offender Register, adopted in Victoria in 2004.

But Mr Barrett said that the latest offences "didn't happen".

"I had to plead guilty because I had a prior ... because it was easier on that little [expletive]," he told Channel Seven.

"He stole from me. That's why he made the lies up, because I caught him stealing."

Mr Barrett said while he admitted he had been convicted of child sex abuse in Queensland, he felt he had been "harassed enough" and was concerned that people would point and say "there goes the paedophile".

Mr Barrett's shop, in Melbourne's south-east, was open for less than six months before he was arrested in February.

He received seven months' jail for offences including groping the victim, showing him pornography and sending him a picture of his genitals.

The victim's sister told Channel Seven she believed setting up the business near the school was a "planned and premeditated" move.

She said the attack had a profound impact on her family.

"He [the victim] wouldn't catch a bus by himself. My parents would need to leave work to take him to counselling. He won't walk down the street by himself. I feel really sorry for him because I know it's going to affect him for the rest of his life," she said.

The victim's mother said it made her "angry" to think that Mr Barrett was allowed to "prey on young children".

In sentencing Mr Barrett, Magistrate Amanda Chambers said he would be added to the sex offenders register and face lifelong reporting obligations.

He was given an immediate prison term with an 18-month corrections order requiring him to undergo treatment.