A Perth couple are on trial accused of starving their 17-year-old daughter to the point she weighed barely more than 27 kilograms and was at risk of having a heart attack.

WARNING: This story contains details some people may find distressing.

The girl was "wasted, with limited body fat" and so malnourished that she was as small as an 11-year-old, the prosecutor said.

The prosecutor said her parents, who can't be identified for legal reasons, refused to acknowledge the concerns, saying she was naturally small and ate "a healthy vegan diet".

Dance teachers raise alarm

The first day of their trial in the District Court heard their daughter, who's now an adult, was home schooled and loved dancing, but had the mental functioning of a much younger child.

It was her dance teachers who raised the alarm, leading to the intervention of WA's Department of Child Protection, and the girl's admission to hospital in 2021.

Prosecutor Jehna Winter said dance school teachers had been concerned enough about her appearance, and lack of physical development, to approach the girl's mother.

But her mother dismissed the concerns, saying she'd been a premature baby and the family had a history of "small stature".

She claimed her daughter was "eating too many carrots" and always ate healthily, Ms Winter said.

Lies about her age

The court heard the girl's parents lied about her age, telling people their daughter was born in 2006, when she was actually born two years earlier.

Prosecutor Winter said that by 2019, the girl's condition deteriorated, and she vomited at a dance class and showed signs of "weakness and fatigue".

Worried about her strength and stamina, a dance teacher refused to enter her in a dance festival and sought to reduce her program.

The teacher, who had a medical background, wanted a health assessment to be conducted before the girl could re-enrol.

The parents resisted, the court heard, with the father saying she was suffering discrimination because she was "skinny and vegan".

They responded by enrolling her in a different dance school — but concerns for her daughter were raised there too.

At that school, a teacher told the mother her daughter's "lack of weight and muscle tone affected her dancing".

The teachers at both schools also had concerns about the girl's behaviour and interactions, the court heard, and she wore bows, frills and clothing that consistent with what younger kids would wear.

A dance costume she wore was a children's size six, the court was told — the same as what one of her teacher's own six-year-old was wearing.

The prosecutor said the girl seemed to have "no independence whatsoever".

Authorities step in

In 2020, the Department of Child Protection opened an investigation into the family.

Attempts to get a medical assessment failed, the prosecutor said, until the girl was taken to see a GP in April 2021.

The father had claimed she'd lost weight due to academic exams, and had allergies.

The court was told her father described her as the "healthiest child that he knew".

But the doctor who assessed her found she was 27 kilograms, and barely more than 147 centimetres tall.

Her body mass index (BMI) was 12.5, when a healthy BMI was 18.25, the court was told.

The doctor wanted her to go to hospital urgently, but the mother resisted, saying her daughter was still distressed about the recent death of her 22-year-old cat.

She was admitted to Perth Children's Hospital days after she saw the GP, and doctors there tried to convince the parents of the need for medical care.

They refused consent for a feeding tube and the department used its powers to bring her under care.

It was determined that she had the average height of an 11-year-old, bone age consistency of a 13-year-old, and delayed puberty.

Health improves in hospital

During her 50 days in hospital, her height increased to 151 centimetres and her weight went up to more than 35 kilograms.

Prosecutor Winter said the then 17-year-old wasn't born premature and didn't have the allergies her father claimed.

Her condition wasn't explained by genetics or hormones, she told the court.

Ms Winter said there were concerns about her social and environmental development, as she liked TV programs like the Wiggles, Teletubbies, Charlie and Lola and other shows preferred by primary age children.

An occupational therapist found that, while articulate, she had a lack of functioning in self care.

The court was told the girl left hospital in May 2021, into the care of a relative.

By February 2022, the court heard, she was more than 41 kilograms and 154 centimetres tall, and had started menstruating.

Her parents have been charged with "conduct that may have resulted in a child suffering".

Before the trial started, the father pleaded guilty to forging her birth certificate.