Inside, their two younger step-siblings were clean and well-cared for. The situation continued for almost a year until police intervened in April, placing the 11-year-old and 13-year-old into emergency foster care.

And on Monday morning, a local father and stepmother pleaded guilty to child neglect charges at Queanbeyan Local Court over what a police report called a "severe case of neglect and psychological abuse."

The 13-year-old and 11-year-old children had shared a two by three-metre room detached from the main house since June last year, with one mattress between them. They were allowed to bathe once a week with cold water from the laundry sink.

The children were under the care of their biological father and step mother at an inner-Queanbeyan residence until police arrived on the evening of Friday, April 11 to check on their welfare.

They found the children alone and unsupervised, living outside in unhygienic conditions and with the 11yo showing signs of malnutrition.

Police interviewed the children at the scene. The 11yo had never been inside the house, while the 13yo reported being allowed inside once to help move furniture.

Shortly after police arrived the parents returned home along with their two younger, fully biological children, who the report noted were "well-dressed, clean and in good health."

Police removed the 11 and 13yo from the scene that night and laid charges against the father and stepmother on April 26.

The 31yo stepmother and 39yo father represented themselves in court on Monday and pleaded guilty to two child neglect charges. The father also pleaded guilty to one charge of assault.

Magistrate Mark Douglass said he regarded the matter "as being aggravated and serious" and adjourned it to June 30 for sentence. He continued an AVO preventing the parents from contacting the two children without supervision.

Meanwhile, police prosecutor Danielle Byrne indicated she'd be seeking a jail sentence for the offences and said it was unlikely the parents would regain custody of the children.