Toddler rarely showed pain: accused mum

A mother accused of killing her two-year-old son told police after his death she had no idea how he fractured his collar bone, ribs or shoulder blade.

But she said he may have suffered broken wrists after jumping off a flight of stairs at home.

The boy, who cannot be named for legal reasons, was two years and seven months old when his stepfather called triple zero on the afternoon of August 3, 2012 and complained the toddler was "limp".

Just over an hour later the boy was pronounced dead at Wollongong Hospital.

His mother, who also cannot be named, is facing a Supreme Court trial after pleading not guilty to his unlawful killing.

The Crown alleges the boy died from blunt force injuries to his head and abdomen likely sustained in the days prior to his death.

The Crown does not allege the mother inflicted the injuries but says her failure to seek medical treatment "substantially caused or accelerated the death of her son".

On Thursday, the jury watched a series of police interviews with the mother in the days after the boy's death.

In one recorded on August 8, she tells them the boy would often return from his father's - who shared custody of the toddler - with bruises.

She said her ex-partner would blame their daughter, saying the girl used to bite the toddler.

In another interview on August 20, the mother said she didn't know how the boy suffered fractures to his collar bone, his shoulder blade or his ribs.

She said he never showed signs of pain, other than once when he walked down the driveway and said "Ow".

"I thought it was just his foot hurting," she said.

When asked if she knew how the boy would have sustained two broken wrists, she said she had seen him jumping off stairs in her partner's home, which would have been about "three-feet" high.

"But I don't remember how he landed," she told them.

The trial continues.