Former Bega Cheese boss Maurice Van Ryn has had his minimum sentence for child sexual assault offences increased from seven years to more than 13 years after an appeal from the crown.

In September last year, Van Ryn was sentenced to 13 years in jail with a non-parole period of seven years for 17 offences committed between 2003 and 2015.

After that sentence was handed down the New South Wales Director of Public Prosecutions lodged an appeal against the sentence, arguing it was inadequate.

Today's decision means the non-parole period has almost doubled to 13 years and 6 months, with his total jail time increased to 18 years.

Including the amount of time already spent in custody, the earliest date Van Ryn will be eligible for release on parole is June 9, 2028.

Van Ryn pleaded guilty to the abuse of nine boys and girls between the ages of eight and 15 on the New South Wales far south coast.

Today's ruling, by Justices Mark Leeming, Peter Johnson and Robert Allan Hulme, found Van Ryn's good character and the fact he sought treatment for paedophilia should not prevail over "the need to impose a sentence that is proportionate to the gravity of a crime".

"The sentence was so inadequate that it warranted the description of being 'an affront to the administration of justice'," the ruling said.

'It feels like this is how it should be': victims' spokesperson

Outside the court today a spokesman for the victim's families said the new sentence set the bar for other cases of sexual abuse.

"We are completely astounded. Astounded because it's beyond our wildest expectations," the spokesman said.

"We have at times felt like we've had to fight and cajole the system to get to the result that we have.

"It feels like this is how it should be. The charmed run has come to an end.

"These people in our local community, who continue to support him and say that he is hard done by, the message that they too need to receive is 'no, he is an evil, evil person and stop supporting him'.

"Stop writing letters to the court requesting that his sentence be reduced. You are as bad as he is if you do that.

"The community needs to be protected. The reason why we took this course was not out of vengeance, but to protect the community."

Today's ruling said Van Ryn had displayed "arrogance and belligerence" and had "understated the seriousness of his offences".

Van Ryn a 'father figure' to victim

It said the offences happened in his house when children would visit to use the pool, spa, tennis court and to play video games.

The ruling said the offences "commonly involved Van Ryn reaching inside the clothing and swimwear of a child and touching their genitals".

"The most serious offences [were] the persistent sexual abuse of a child which occurred over a 5-year period and concerned a boy who at the beginning was aged 11," the finding said.

"Van Ryn befriended him, gave him gifts, soft drinks and lollies and also gave him money for performing odd jobs.

"The sexual contact commenced with Van Ryn sitting next to the child and rubbing his upper thigh.

"It progressed to touching his genitals when they were together in the spa.

"The behaviour further progressed to oral and anal intercourse, on some occasions after showing pornography to the child."

In the original sentencing, Judge Clive Jeffreys had given Van Ryn a 25 per cent reduction for pleading guilty at the earliest opportunity.

In September, the court heard Van Ryn had ingratiated himself with his teen victims and was "a father figure and role model" to at least one boy he abused.

Van Ryn had formed a friendship with one of his victims when the boy was just 10 years old and being bullied at school.

At the time of the original sentencing, the father of one of the victims, who can not be identified for legal reasons, said Van Ryn's jail sentence needed to be challenged to prevent other paedophiles getting off lightly.

Judge Jeffreys told the court he did not take grooming into account in ruling on the case.