A boy with autism died after his parents allegedly attempted to calm him down by giving him a cold shower, strapping him to a chair and leaving him in a garden shed where temperatures dropped as low as five degrees, a court has heard.

The 11-year-old boy's mother, who can not be named for legal reasons, faced Sydney's District Court on Wednesday after she was charged with manslaughter following her son's death on October 1, 2011.

The court heard that the woman and her partner, the boy's step father, had started struggling to care for the young boy, who had difficulty sleeping and suffered from outbursts where he would throw himself around, the Sydney Morning Herald reported.

The 11-year-old boy's parents strapped him to a chair and left him in the garden shed on the night he died

Crown prosecutor Peter McGrath SC said the boy's parents had started to restrain him in times of difficulty, using packing tape on his arms and legs and a 'a belt or ratchet type tie' around his waist.

On the night of the boy's death he was bound to a chair and placed in the garden shed at the rear of the family home in central west NSW, according to reports.

The court heard that the step-father picked up the boy, who had been 'unsettled', and placed him in a cold shower - a technique his mother said had been an effective method to 'snap him out of it'.

The mother had been sleeping when her husband placed her son outside and woke to his screams before she found her son's limp body in the chair, with his tongue protruding from his mouth.

On the night of the boy's death he was bound to a chair and placed in the garden shed at the rear of the family home in central west NSW

The boy's parents had started to restrain him in times of difficulty, using packing tape on his arms and legs and a 'a belt or ratchet type tie' around his waist

The mother told police in 2011 that she feared her son would hurt himself and had been trying to do the 'right thing'

The court heard that temperatures dropped to five degrees that night and the boy, who was wearing tracksuit pants and a jumper, weighed only 24 kilograms and had been unable to retain warmth.

The crown alleged that the cold conditions, coupled with the boy's inability to remove the wet clothes or put on any others, directly contributed to his hypothermic condition, the Sydney Morning Herald reported.

'He was at the will and mercy of his mother and her husband, who was also in a position of parental responsibility to the boy,' Mr McGrath said.

While the mother was sleeping at the time her son was placed in the shower, the prosecution maintains that she was still jointly responsible as she had been aware of the method and had previously consented.

The court heard that from 'time to time' he was placed in the shed (pictured), with a baby monitor set up to ensure the couple could still oversee his care

The court heard that the step-father picked up the boy, who had been 'unsettled', and placed him in a cold shower - a technique his mother said had been an effective method to 'snap him out of it'

According to reports, her lawyer told the court that she believed her husband would provide 'whatever care' the boy needed.

Mr McGrath said the couple feared the 11-year-old would harm himself and had previously restrained him using plastic pipes and a sleeping bag, sometimes forcing him to sleep upright bound to a chair, the Sydney Morning Herald reported.

The court heard that from 'time to time' he was placed in the shed, with a baby monitor set up to ensure the couple could still oversee his care.

The mother told police in 2011 that she feared her son would hurt himself and had been trying to do the 'right thing', according to reports.

'We have had to restrain him time and time again with tape so he doesn't get up and hurt himself. We are trying to prevent him from hurting himself.'

The trial continues.