SYDNEY - AN AUSTRALIAN couple who imprisoned a six-year-old boy in a baby's cot in their garage were on Friday jailed by a judge who described their behaviour as cruel and bizarre.

The pair kept the child in a portable cot covered with a homemade plywood lid that the boy was unable to remove.

The boy was given water and fed once or twice a day. He was also given a screwdriver and saucepan to bang together when he needed to use the toilet, Perth District Court heard.

'The only light... was sunlight coming under the garage door', Judge Frederick Speight said.

When found by authorities in November 2007, the child weighed only 12 kilogrammes, had little muscle strength and several bruises.

Reports said he had been kept in the cot for as long as two years.

'If the situation had continued much longer, then (he) may have died,' Mr Speight told the court, national news agency AAP reported.

'As a six-year-old boy, he had no capacity to resist'.

The court heard that the 34-year-old woman had become the boy's foster mother soon after he was born, when his natural mother was unable to care for him.

The woman, who cannot be named for legal reasons, began to resent the boy because he was not her own and placed him in the cot to keep him away from her five natural children, who were all well-cared for, the court heard.

The woman was jailed on Friday for two years and eight months for reckless neglect of the boy while her 31-year-old husband received a maximum sentence of three years and two months for assaulting the boy, AAP said. -- AFP