A Melbourne woman who repeatedly had sex with a 13-year-old boy-next-door and had three of his children has escaped jail.

The woman, who cannot be named, started having sex with her teenage neighbour in August 2004, when she was 22.

Victorian County Court Judge Christopher O'Neill sentenced her to three years in prison, wholly suspended for three years.

The woman now has six children and Judge O'Neill said her family circumstances had to be taken into account in the sentence.

"Normally offending of this seriousness would warrant a significant jail sentence," Judge O'Neill said on Friday.

"(But) there is a discretion to the court to grant special mercy where the circumstances of family hardship are exceptional."

Judge O'Neill said the woman's husband worked full time to support the children.

"I accept that almost every waking moment is spent looking after the children in one way or another," he said.

The woman, now 32, pleaded guilty to maintaining a sexual relationship with a child under the age of 16.

Judge O'Neill said the woman gave the boy alcohol, drugs and freedom, but that was not evidence of grooming or predatory behaviour.

He said the woman had an IQ of 64 and showed the cognitive ability of a teenager.

The boy was 13 when the pair started having sex. They lived together for a time and had their first child when he was 15.

The couple had two more children before they split up in 2009.

The boy reported the relationship to police in November 2011, but the woman wasn't interviewed until July 2012.

Judge O'Neill said the woman would be on the sex offenders register for life.

AAP