The grieving parents of a toddler who drowned in a backyard swimming pool weeks after he was taken into temporary foster care in Sydney's north-west say their son should never have been placed in a home that was unsafe for children.

Johnny Slager and Vanessa Lewin are demanding answers about alleged shortcomings in the state's foster care system after their 22-month-old son, Braxton, died at the home in Stanhope Gardens, near Kellyville, in September last year.

Braxton's foster carer found him floating unconscious in the small backyard pool on September 13 and, despite desperate attempts by a neighbour to resuscitate him, he was pronounced dead at The Children's Hospital at Westmead that day.

An autopsy report said police who attended the home found that the pool fence did not have a self-latching gate and that the home was "not safe or secure for young children placed under foster care", according to the ABC's 7.30 program.

Police photographs, which Mr Slager said he obtained from the coroner, also allegedly showed beer cans, medication and rubbish strewn throughout the home and its backyard.

Braxton's parents are now demanding how a system designed to protect vulnerable children could have led to their beloved boy's death.

They have posted their son's story, and photographs of the foster home in which he was living, on social media to highlight the system's alleged shortcomings.

"I loved him so much. I miss him so much. He was my beautiful, beautiful little man," Mr Slager said, breaking down, in an interview with 7.30 on Thursday night.

Mr Slager, who had previously been Braxton's primary carer, told the ABC that he contacted the Department of Family and Community Services for help to care for his son last year because he intended to withdraw from methadone.

When Mr Slager started experiencing "some medical issues", he claimed the department told him he had to place his son in foster care, otherwise the department would seek permanent custody of Braxton.

Ms Lewin felt incapable of looking after her son because of her own drug use, the ABC reported.

A non-government organisation, Life Without Barriers, then placed Braxton into the foster home in Stanhope Gardens. Life Without Barriers is contracted by the department to place children into foster care.

Braxton was reportedly in foster care for about three weeks, and was just days away from returning to his father, when he drowned.

A mandatory inquest is yet to be held into his death.

Life Without Barriers told Fairfax Media on Friday that the organisation's thoughts were with Braxton's family.

However, a spokeswoman for the organisation said she was unable to comment further on Braxton's case while it was being investigated by NSW Police, and before a coronial inquest was held into his death.

A date for the inquest had not been set, she said.

"We are an accredited provider in every state and territory, and the well-being and safety of children across Australia is our priority," the spokeswoman said.

"We will continue to monitor and review and consider any recommendations of any inquiry to make sure we have everything we can in place."

Ms Lewin told the ABC of having to go to hospital to identify the body of her son.

"And just seeing him dead on the table ... ," she said, breaking down.

Braxton's funeral, she said, was "the worst day of my life. I never imagined I'd have to bury my child."

Joe Tucci, a child protection expert at the Australian Childhood Foundation, told the ABC the photographs of the foster home were deeply concerning.

"If there was a baby, a toddler, in this kind of environment, it would be a huge danger to them; there is no way that I would have ever allowed a foster carer to remain in this type of environment. In fact, I don't think many foster care agencies and workers today would allow this to occur," he said.

The Department of Family and Community Services told the ABC it was "saddened" by Braxton's death, but could not comment further as the matter was before the coroner.