The mother of a young girl who requested a new swimming teacher after saying he had inappropriately touched her twice thought it may have been an accident.
But then her second daughter complained of the same teacher touching her private parts during a lesson, and also asked to change out of his class.
The two sisters' pre-recorded evidence was played in the NSW District Court before their mother testified on Tuesday, saying her youngest daughter described the assault like a "worm inside of her".
"She said she squeezed her legs together for the rest of the lesson so it couldn't happen again," the mother said.
Kyle James Henk Daniels, 22, has pleaded not guilty to 26 charges, including multiple counts of having sexual intercourse with a child under 10 and indecently assaulting a person under 16.
He is accused of touching nine of his students aged between 5 and 10 on or near their genitals while instructing them between February 2018 and February 2019 at a Mosman pool on Sydney's north shore.
In a police interview last year the youngest daughter said she was lying on her back in the water using a kickboard to stay afloat and with her legs slightly apart.
She says her teacher pushed her private part "very hard and it hurt," and something felt wrong so she inspected the area.
After pulling her swimming costume out from inside her, she felt a lot better, she says.
When asked what it felt like she responds saying "a little bit sore and a little bit like a worm was in it".
Straight after the incident she approached her mother and told her there was something private she wanted to tell her alone.
Her mother asked her to wait until they leave the swimming centre where she sat and "had a think about what he did when I was kicking on my back".
"So I hold it in my head and then I got a chance to tell her ... near when it was at dinner time."
The girl's complaint is one of several charges Daniels faces for sexual intercourse with a child under 10.
It comes after her older sister was heard on Monday saying Daniels had touched her inappropriately twice in the same pool, about two weeks earlier.
The girl wrote a note immediately after which read: "The reason I didn't like my swimming lesson was because my teacher touched my...."
She later explained the missing word was "vagina".
Her mother told the court she asked the girl whether she thought it was deliberate, to which she replied: "I could understand if it was an accident if it happened once but why would he do it again?"
But after her second daughter complained about Daniels, the parents informed the swim school, with the mother saying she had "assumed it had been an accident".
"But now this had happened, that's why I was mentioning it."
She never saw her daughters discuss the separate incidents and both girls say they were too embarrassed to tell their siblings.
This formal complaint to the swimming centre sparked the police investigation into similar accusations.
The trial continues before Judge Kara Shead.