The New South Wales director of public prosecutions (DPP) has lodged an appeal against the sentence given to convicted Bega paedophile Maurice Van Ryn.

The ABC understands the DPP will argue the 13-year sentence given to the former Bega Cheese chief executive for multiple child sex offences was inadequate.

Van Ryn pleaded guilty to the abuse of nine boys and girls between the ages of eight and 15.

The sentencing judge gave him a reduction on his sentence for pleading guilty at the earliest opportunity and gave him a non-parole period of seven years.

Justice Clive Jeffreys referred to Van Ryn's previous good character, contrition and the fact that he had sought psychiatric help.

The father of one of his victims, who cannot be named for legal reasons, said his jail sentence must be challenged to prevent other paedophiles getting off lightly.

He said even if Van Ryn's sentence was not increased, the judge's comments needed to be tested.

"There were so many statements that the judge made as to why he was reducing Van Ryn's sentence," the victim's father said.

"The danger is that if these things are let to slip through then other child sex offenders will use these precedents to have their sentences reduced.

"Even if it doesn't result in a longer period of sentence for Van Ryn, suggestions that because he was a good corporate citizen that he should somehow be given a lesser sentence, untested claims he suffers from adult ADHD, it can't be let to be precedent for future cases."

Van Ryn has been told of the appeal and the matter will appear in court next month.