Peter Leishman, 69, pleaded guilty on November 23 last year to two rolled up charges of sexual penetration of a child under 16 and one charge of indecent act with a child under 16.

On February 21 he was jailed for six years.

He must serve a non-parole period of three years and four months.

Judge Kellie Blair said Leishman was aged between 39 and 44 when he sexually assaulted two young girls over a five-year period from mid-1990.

She said the man had befriended the mothers of the victims, who were aged between five and 10 at the time of the offending.

The court heard the first victim was sexually penetrated by the man while under his supervision and care and at various locations, including in a caravan, a sport stadium in Warrnambool and at the house of the second victim.

The second victim was assaulted by the man about 10 times over a three-year period while she was swimming at a Warrnambool caravan park.

Leishman was interviewed in 2016 and charged three years later while he was in jail for unrelated offending.

Judge Blair said it was clear Leishman's offending had a "devastating and lifelong impact" on the first victim, who turned to drugs and alcohol to numb her pain and continued to suffer poor mental health.

Referring to the second woman's victim impact statement, the judge said Leishman had robbed her of her ability to trust.

"This has negatively impacted her ability to engage and maintain relationships that are healthy, positive and strong," she said.

The court heard Leishman had a relevant criminal history, including possessing child abuse material and stints in jail for charges of indecent assault.

Judge Blair said sexual offending against children was "abhorrent".

"Children are one the most vulnerable groups in society and there is a presumption that children will be harmed and must be protected from sexual exploitation and premature sexual experience of all kinds," she said

The judge said Leishman's victims were vulnerable and often left in his care.

"Your offending represents a gross breach of trust, firstly because of the very young ages but also as a result of your relationship with each of them," she said.

She said the penetrative acts against the young girl were "repeated and depraved."

Judge Blair said an "inadequately explained" three-year delay in the case meant Leishman missed the opportunity for concurrency (a jail sentence that is served at the same time as another sentence).

She said it also interrupted the rehabilitation he "desperately require".

"The delay has also resulted in your return to custody after being at liberty for three years which must be extremely difficult," the judge said.

Leishman had served 90 days in custody at the time of sentence.

He remains on the sex offender registry for life.

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