Harrowing pictures show how an Australian toddler fed on an extreme vegan diet by her parents became so malnourished she 'looked like she lived in the Third World'.

Photographs shown to a Sydney court, where the child's mother and father face prison, show the girl in intensive care after she was finally taken to hospital for the first time, when she suffered a seizure aged 19 months.

At the time she had no teeth, could not stand up, weighed less than 5kg (11lbs) and looked like a three-month-old.

The child, who was fed a diet relying on oats and rice milk, was 'defenceless and unable to protect herself from her parents, and developed rickets.

She was eventually put into foster care with her two older brothers, then aged four and six. But her foster carer said the little girl is now obese and it is as if she was 'storing up calories' in case she needs them in future'.

Details of the child's neglect were revealed in Downing Centre District Court on Thursday during a sentencing hearing for her parents.

This 19-month-old girl looked more like a three-month-old and weighed less than 5kg when she was taken to hospital in March last year. She was fed an extreme vegan diet by her parents

The child, who was diagnosed with the degenerative bone disease rickets after being taken to hospital for the first time since her birth, is pictured above in an intensive care hospital bed

Father, 35, and mother, 32, of a toddler who was so malnourished she was suffering from rickets, a degenerative bone disease caused by a lack of vital nutrients

The court has heard the toddler, now almost three, had no medical records after her birth and had never been vaccinated.

Neighbours did not even know the child existed, the court was told.

The couple's daughter was eventually put into foster care and is now obese while her carer says the youngster 'immediately stands out as different from other children'.

The girls' parents are facing up to five years in prison in a case of sustained neglect which each of their lawyers has called 'tragic'.

The father, who has split from the mother since the couple's arrest, has described her as the child's principal carer and said she dictated her diet.

The mother, who claims she was depressed after her daughter's birth, says the girl was well looked after in all ways other than nourishment.

She has now lost custody of all three of her children and is deeply remorseful.

Judge Sarah Huggett noted the father had failed to notice his daughter could not walk or talk and rejected his claims he was acting under the direction of his partner.

The toddler could not crawl or even roll over when first taken to hospital. She has now learnt to stand and walk after intensive rehabilitation but is a long way from making a full recovery

'He must have realised at 18 months that she wasn't reaching the milestones she should have,' Judge Huggett said.

'He did nothing... He could have picked that child up and driven her to a doctor.'

Barrister Ben Clark, for the mother, said the case had torn the family apart.

'At first glance people are going to say, "What sort of mother is she?"' Mr Clark said.

'The mother let her down and let her down terribly.'

However, Mr Clark said his client was suffering from depression and her behaviour was 'reckless' rather than deliberate.

'There is no evidence she's some kind of anti-vax crackpot,' Mr Clark said.

Frank Coyne, for the father, said what happened to the child was 'a truly tragic set of circumstances... for the whole family.'

Until the child suffered a seizure in March last year she had appeared to the father as 'someone who was happy, engaged and bright.'

Mr Coyne said the father ate meat and dairy products when he was not at home and that the case should not be a 'vegan and anti-vax witch hunt'.

Julia Dewhurst, for the Crown, said examples of such serious malnourishment in a child were rare in Australia and were more likely to be seen in a Third World country.

The child's parents pleaded guilty to failing to provide for a child and causing serious injury due to recklessness. The mother is pictured outside court on Thursday afternoon.

The girl's mother and father, aged 32 and 35, admitted to failing to provide for their child, causing her serious injury.

They fed the girl a diet so lacking in basic nutrients she developed rickets, a degenerative bone disease caused by a shortage of vital nutrients.

Neighbours told police they saw only the girl's two older brothers playing in their backyard and did not know the couple had a third child.

For 19 months authorities had no idea of the neglect the toddler was going through until she had a seizure at the family's home in Sydney's eastern suburbs.

The girl stayed in hospital for a month in March last year with her mother constantly by her bedside.

A victim impact statement written by a foster carer on the child's behalf revealed the extent of her malnourishment.

'For the first 19 months of her her life (the girl) did not receive the basic care to grow and develop,' the carer said in her statement.

The toddler (pictured after she was taken into care) was so malnourished by her parents she looked like she lived in the Third World

'[The girl] was defenceless and unable to protect herself from her parents.'

When the carer first encountered the child she was 19 months old but weighed less than 5kg and looked like a three-month-old.

She was shocked by how far the girl was behind in her development.

The child, who had no teeth, could not sit up or even roll over, let alone use her hands for simple tasks such as playing with toys.

'Caring for [the girl] was like caring for a very young baby,' the carer said.

The child, now almost three, had made progress but her height and weight were out of proportion.

'The gains have not come easily,' the carer said.

'This crime has had a long-term impact on her development.'

The girl could now crawl, stand and walk and spoke about 20 words.

She had developed a healthy appetite but her short stature meant she was obese.

'It's like her body is storing calories in case she needs them in the future,' the carer said.

'She immediately stands out as different from other children,' the carer said in her statement.

The court has previously heard the mother behaved 'generally normally' when the child was first taken to hospital.

The mother told police the child was a 'fussy eater'. Sometimes for a snack the child was given a mouthful of fruit or two sultanas (the parents pictured outside court)

She would at times 'not engage' with her daughter but fed, changed and comforted her when staff asked her to do so.

The mother told a hospital dietitian her entire family followed a vegan diet and detailed the extreme eating measures that led to the girl's condition.

She said her daughter would generally have one cup of oats with rice milk and half a banana in the morning, and a piece of toast with jam or peanut butter for lunch.

For dinner, she said her daughter would be offered tofu, rice or potatoes.

But she said the girl, who was also breastfed once day, was a 'fussy eater' so she might just have oats again.

Sometimes for a snack the child was given a mouthful of fruit or two sultanas.

This diet resulted in severe deficiencies in nutrients for the infant, including a lack of calcium, phosphate, vitamin B12, vitamin A, iron and zinc.

Her levels of vitamin D - which can cause bone disease if found to be too low - were 'undetectable'.

The girl is now considered obese because her height and weight are so out of proportion

The infant had fractures throughout her tiny body and her bones were so brittle doctors believed they could have been broken by 'normal handling'.

The girl had little documentation and no medical records after she left hospital in 2016 after being born in 'good condition'.

The mother had a water birth and discharged herself just three and a half hours after delivery. She returned for a post-natal check three days later.

WHAT IS RICKETS? - Rickets is a disease causing soft and weakened bones in young children - The disease is caused by a lack of Vitamin D, calcium or phosphorus - Vitamin D deficiency can be caused by diet or inadequate sunlight exposure Signs and Symptoms: - Painful bones, muscle weakness, cramps and spasms - Slowed growth and development - Increased risk of broken bones, including spontaneous breaks that occur by themselves without pressure or trauma - Dental problems such as teeth failing to form or being slow to emerge, deformed teeth or soft tooth enamel - Prominent forehead and a large front fontanelle (soft spot) in infants - Deformities of the skeleton such as bowed legs, kyphosis ('hunch-back'), scoliosis (sideways curves of the spine), outward jutting breastbone or abnormal skull shape Source: Victoria State Government Advertisement

However, the mother then refused a newborn screening test or a hearing check, telling doctors she would rather her GP do them.

She never saw the GP for the tests and ignored multiple phone calls, voicemails, text messages and a letter for two weeks.

'The hospital discharged (the mother) from their care after no response was received,' court documents read.

The father told told Family and Community Services the couple 'did not want to put her through immunisations as (it was) hard on baby.'

The treatment of the girl was only brought to the attention of doctors in March last year when doctors attended to the infant after she suffered a seizure.

One doctor described her as 'floppy' and noted how the diminutive one-and-a-half year old didn't crawl or talk during a month in care.

Hospital staff initially respected the parents' wishes to keep the infant on a vegan diet, but grew concerned when the mother outlawed soy because it was full of 'hormones'.

Even after the girl had been hospital for a week, the parents exchanged text messages denying their daughter's lack of growth was a result of malnutrition.

Soon after, police spoke to the father at the hospital, asking him why he wasn't concerned that his daughter never grew.

Even at more than a year old, the child weighed only 4.9kg, barely double what she weighed when she was a newborn.

'[The father] thought she was a girl and different to boys - she was petite,' court documents said.

The mother (pictured with her husband) told a hospital dietitian her entire family followed a vegan diet. She said her daughter would generally have one cup of oats with rice milk and half a banana in the morning, and a piece of toast with jam or peanut butter for lunch

After an investigation into the girl's medical history, doctors found an absence of immunisations, no follow-up check-ups after she was born and no birth certificate or Medicare number.

Within six months of being taken into foster care the girl had put on 6kg and was crawling and standing on her own.

But doctors said it was still 'imperative' she continued therapy and was constantly monitored to help manage developmental delays.

The parents pleaded guilty to failing to provide for a child and causing serious injury; charges of reckless grievous bodily harm were withdrawn.

The girl now lives with a relative and her two brothers in another state.

The sentencing hearing was adjourned until June 28.

The mother and father (pictured hugging) leaving court last year after pleading guilty to causing serious injury to their toddler after feeding her an extremely restrictive vegan diet