"One can only imagine how distressed they would've been when they put two and two together," Mr Cordwell said.
On the day of the attack, Horne had been at a barbecue with family and friends but excused himself.
He spent some time in Glendene Ave Reserve smoking cannabis and watching three girls playing.
Horne attempted to join their dancing, at one point offering them chewing gum.
As the group walked away, he grabbed one of them and ran with her through the bush to a creek bed where he undressed her.
He tried to stifle the girl's screams by putting his hand over her mouth but her mother heard and followed the noises.
Judge John Bergseng said her quick response limited the seriousness of the indecent assault and the 6-year-old escaped with scratches to her torso and legs as Horne bolted.
However, a victim impact statement highlighted the ongoing effects on her which included a mistrust of young men and a reluctance to go anywhere without her parents.
"Her mother rarely sleeps through the night and they find themselves asking whether or not anyone interacting with their daughter might be a secret paedophile," the judge said.
Horne's parents also partially blamed themselves for what happened.
Months before the attack, the offender's father had found some "disturbing images" on their computer but when he confronted his son, he vowed it would not happen again.
A doctor's report confirmed Horne had a sexual interest in young children and assessed him as a moderate risk of reoffending.
However, the 20-year-old said he would be open to counselling to address his urges.
Horne, who has been deaf since birth, was aided by a sign-language interpreter in court.
Judge Bergseng took acknowledged his early guilty pleas, his disability and the young man's family support in sentencing him.
