Devonte Mulitalo gave his victim a picture of them together so she could remember him.

The family of a 12-year-old girl who was groomed by an after school care worker are "gutted" Crown Law won't be appealing his sentence.

In November, Devonte Mulitalo, 23, from Auckland's Glen Innes, was sentenced to 11 months' home detention by Judge Mary-Beth Sharp and placed on the Child Sex Offender Register.

The offending was the parents' worst nightmare - a sexual predator disguised as a youth worker.

She was 12, he was 21. She trusted him, her parents trusted him, his employer trusted him.

But while she was in his care, Mulitalo groomed the girl, told her he loved her, made her perform sexual acts on him and sent explicit videos and text messages to her.

SUPPLIED Devonte Mulitalo posted a picture to his Instagram of him in a prison inmate's outfit a few weeks before he was sentenced.

Mulitalo groomed the young girl between December 2016 and July 2017 while the victim was in his care at a programme run by Youthtown in Auckland.

After Mulitalo's sentencing, a petition calling for him to be resentenced and sent to prison gained more than 28,600 signatures.

Soon after, the Crown prosecutor lodged an appeal against the sentence.

However, on Friday, the victim's parents were told Crown Law would not longer pursue the appeal.

The father told Stuff the news was really "gut-wrenching".

"We're feeling really numb and a bit lost," he said.

A spokesperson for Crown Law said the Deputy Solicitor-General (Criminal), as well as two other Crown counsel, had reviewed the sentence imposed on Mulitalo in the District Court.

"No error of principle is apparent in that sentence. Nor does it reach the threshold of being manifestly inadequate," the spokesperson said.

"In the circumstances, we do not consider there is any basis for an appeal. The police have this morning advised the victim's family of the Deputy Solicitor-General's decision."

Hours after he was sentenced, a video emerged on Instagram of Mulitalo dancing and celebrating, which "disgusted" the parents of the victim.

As part of his home detention conditions, Mulitalo is banned from having contact with anyone under the age of 16 and is not allowed to own, possess or use a device with internet access.

Community Corrections staff interviewed Mulitalo about the video and said they were satisfied the clip was filmed by a family member earlier this year. It has since been deleted.

Prior to Mulitalo's sentencing, Stuff was also sent a picture of him dressed in a Halloween prison inmate costume, gloating about how he was dodging a prison sentence.

The post said: "When y'all thought I was going in but then the game changed. #wegood"

That picture was passed on to the Crown prosecutor and the police ahead of the sentencing.

"I saw his photo ... this guy (Mulitalo) is just laughing his way. I'm fuming and furious," the dad said.

A letter of apology Mulitalo wrote to the victim was handed up to Judge Sharp in court.

At his sentencing, Mulitalo's lawyer, Panama Le'au'anae, said his client now showed deep remorse and insight into his offending.

"He was only 21 at the time and that does not excuse his behaviour ... but could be why he went down that path," Le'au'anae said.