A mother who falsely told authorities that her seven-year-old son died after he had fallen off a pogo stick has pleaded guilty to his manslaughter, in one of the worst child abuse cases recorded in Australia.

Court papers revealed that the boy had been dead for some time - and rigor mortis had set in - before paramedics were called, and that he had suffered months of horrific abuse at the hands of his 26-year-old mother and, it will be alleged, her new God-fearing boyfriend.

Between January 2013 and his death in May that year, the boy was starved, beaten, forced to wear nappies, separated from his family and forced to run on a beach until the point of exhaustion.

In the months leading up to his death he was also forced to eat his own faeces, stand on a coffee tin for hours and undergo ‘boot-camp’ style punishment.

The 26-year-old mother, who cannot be named, has now pleaded guilty to a litany of charges

When the seven-year-old finally died, wasted away, covered in bruises and his bones riddled with fractures, it brought an end to four months of horrifying physical torment, humiliation and abuse by the people he loved and trusted the most.

The boy, who was found dead by his mother the morning after she had ‘made love’ with her boyfriend near where he lay dying on the couch, had started off the last year of his life in good condition.

The physically small second grader was described as a ‘very quiet, timid, gentle, softly spoken child with a docile nature’ and good toilet skills and hygiene who had overcome a moderate intellectual disability to enter second grade in a school in Sydney’s southern suburbs at the beginning of 2013.

The seven-year-old boy suffered months of horrific abuse at the hands of his mother and allegedly her new boyfriend

Video footage taken by his mother and her partner would chart the sickening reign of terror that would turn him into a cowering, fearful child weighing just 20kg and his body a mass of bruises, infected wounds and both fresh and healing bone fractures.

The mother, who was separated from the father of the boy and his two younger siblings, a sister, 5, and brother, 4, went to live with a new man less than a week after meeting him.

The children moved in with their mother to a windowless studio without bathroom or toilet, which were only available as shared facilities in the commercial block in a southern Sydney suburb.

Soon after the woman began adopting religious views and a parenting philosophy of toughening the kids up in the way of the Spartans, as seen in the movie 300.

Separated from the father of the boy and his two younger siblings, the mother went to live with a new man less than a week after meeting him

But it was the eldest child who copped all the discipline.

On February 20, travellers on a train from Town Hall in Sydney to the southern suburbs observed the mother using a ‘very hard and aggressive’ tone with the boy as she put him through his paces with the alphabet.

The boy, who was only to attend 12 days at school during the majority of the four months leading to his death, recited the first five letters of the alphabet, but when he couldn’t get past ‘E’ was slapped ‘very hard’ by his mother repeatedly.

During months of abuse the child was starved, beaten, and forced to eat his own faeces

Observers said they felt ‘physically sick’ as they watched the woman slap him an, in the end, the kid just presented his arm up to his mother to be hit.

Video footage of the children in the studio during February shows repeated attempts to get them to confess that their father or maternal father had sexually molested them, to little avail.

During February and into March, things began to turn bad for the seven year old as he was turned upon and became the target of humiliation and abuse.

In one video, the little boy’s brother and sister are encouraged to hit him as he shows obvious pain and fights back tears as he is being taunted for ‘faking’.

The mother (left) originally said her son had fallen off his pogo stick and hit his head

As his brother slaps the boy in the face again and again, he is told , ‘Oh it’s fun. You’re having fun’.

As the victim gasps for breath, he is taunted with ‘that didn’t sound like a soldier to me’ and his brother is encouraged ‘give him a punch in the belly'.

Thereafter the boy’s siblings are encouraged to circle him and punch and hit him as an adult in the background shouts ‘Yeah’ at every strike and the younger sibling is egged on with, ‘Tell him we’re going to do this from now on’.

The mother's boyfriend allegedly also played a major part in the child's systematic abuse

In March the children went on a camping holiday at Bulli Beach south of Sydney, where other campers observed the boy distressed, sobbing and being yelled at for wetting or soiling his pants, and having ice put down his pants.

One woman saw the starving boy being forced to watch his siblings share a bacon and egg roll while he got nothing, and being fed only bread and water while the rest of the family had chicken rolls and cordial.

When the campers called Wollongong police to the tent site, the officers were told that the family was escaping sexual assault by the family of the children’s mother.

When they attended a church service in the Illawarra area on April 7, 2013, the pastors noted that the mother introduced only her younger two children and that the older boy looked sick, pale and had a shaved head and was ‘dressed like an old man in a grey suit’.

According to his five-year-old sister the boy ‘hit his head on the toilet’ and was hit on the head with a wooden spoon while being made to eat his own faeces.

She said the boy was made to ‘eat his poo and he got sick. He'd vomit and [name deleted for legal reasons] smack his face’. She said the boy ‘was crying’ and was told ‘to eat his poo again’.

At 6.12am on May 21, the mother called an ambulance.

This is the message she left: ‘Um, last night, oh yesterday afternoon my son was playing on a pogo stick he banged his head pretty hard. I cooled him down with water … and, um, he’s been sleeping, and I’m just, he’s not moving.’

Ambulance officers found the boy unresponsive and he was pronounced dead. When emergency services arrived the boy was in rigor mortis.

An autopsy found he died from swelling on the brain caused by a large haemorrhage, of the kind treatable when medical assistance is sought. He also showed signs of older injuries, including broken ribs and fractures to his left foot and a finger.

The seven-year-old boy suffered abuse at the hands of his mother (right) and allegedly her new boyfriend (left)

The horrifying details surrounding his death emerged on Tuesday when his mother pleaded guilty to a number of charges, including manslaughter, reckless wounding in company and possessing and disseminating child abuse material.

She also pleaded guilty to using a child in her care to produce abuse material. The Crown withdrew the charges of murder and neglect.

The mother, who cannot be named, pleaded guilty to more than a dozen charges when she appeared via video link from Silverwater Correctional from jail at Central Local Court on Tuesday.

She is set to appear in the Supreme Court in May.