A teenage girl allegedly starved by her parents in Perth told hospital carers she "never had a voice", the WA District Court has heard.

In court on Monday, concerns about the underweight teenager's lack of independence seemed to be confirmed when it was discovered she could not even peel a banana.

The 16-year-old was malnourished, weighing not much more than 27 kilograms when she was admitted to Perth Children's Hospital in April 2021.

One of the concerns that emerged during her hospital stay was an apparent lack of independence from her parents.

Girl voiceless

When nursing staff asked her to use her own voice, to express her own wishes, she responded: "I've never had one of those."

When pressed on what she meant, she said:

The evidence came from senior social worker Denise McNab, who was reading out case notes at the trial of the girl's parents, who are accused of conduct that caused their child to suffer.

The court heard how the girl came into the care of the Department of Communities after the parents refused to allow a feeding tube for their daughter at the hospital.

Case notes recorded that the father did not think his daughter's health was at risk, and claimed the feeding tube was making his daughter want to eat more, "like a junkie".

The court heard both parents said the daughter was "becoming addictive".

Nevertheless, feeding efforts continued with and without a tube until the girl was discharged from hospital.

Weight gain a challenge

Prosecutor Jehna Winter asked Ms McNab how the girl, who was now 17, looked when she was discharged from hospital.

"She had a fuller face," Ms McNab said.

"Happy and healthy.

"Her colouring was good," she said, referring to the "yellowing" that was observed when she was admitted to hospital.

Discussions about whether the girl could go to shops by herself made her nervous but Ms McNab said she was starting to have a "bit more of a voice".

There were still some issues after she was released to the care of extended family, since the Department of Communities retained legal guardianship and continued making decisions about her health.

Ms McNab said the girl still needed to put on weight to ideally get to 45kg, and this was a challenge as she remained on a vegan diet.

There were efforts to enhance her social skills.

Case notes said the girl "did not know how to peel a banana" and "didn't know what to do at a supermarket".

The court heard when she came back from visits to a psychologist, she would be upset and say: "This is all my fault."

Communities closed the file in early 2022, Ms McNab said.

Concerns over re-traumatising girl

The court also heard from Detective Sergeant Brock Tucker, who arrested the parents in April 2021.

He said police acted on the medical observations of the girl that she was malnourished.

Detective Tucker revealed he did not speak to the girl at any point.

When prosecutor Jehna Winter asked why the girl was not interviewed, Detective Tucker said police believed she may not have been able to "withstand" it.

He said police were concerned an interview could "re-traumatise" her, and the "cons definitely outweighed the pros".