Mother said boy was 'faking it': Maybir

A Christian hip-hop producer accused of murdering his then girlfriend's seven-year-old son joined in assaults on the boy because he was "increasingly infatuated" with her, his defence claims.

The boy, who cannot be named for legal reasons, died in Sydney in May 2013 after suffering blunt force injuries to the head.

His mother, Kayla James, has previously been sentenced for his manslaughter.

Kodi Maybir, meanwhile, has pleaded guilty to his manslaughter on the basis of criminal negligence but denies the crown allegations that he murdered him by inflicting the fatal injuries.

James, the crown says, quickly became influenced by Maybir after she met him in January 2013.

She began adopting some of Maybir's "extreme" religious and following his "bizarre" system of controlling her children, which included "varying kinds of punishment" particularly directed at the eldest, now dead, boy.

"She will say he considered her to be a poor parent and the children weren't disciplined enough," crown prosecutor Christopher Maxwell QC said on Thursday.

"She will say she was desperate and believed she was in love with him."

But Maybir's defence barrister Grant Brady SC said this was not a case of the Christian hip-hop producer imposing himself on James but rather his infatuation with her.

Shortly after he met James she became "increasingly aggressive towards her children".

On one occasion he said his client did hit the boy with a spatula because he was becoming "increasingly infatuated with James and started doing things she was doing".

Maybir cried in the dock as Mr Brady said that the boy and his client "both loved wrestling".

They were doing this at Maybir's music studio in Sydney's west in May 2013 when the boy grabbed a hold of his client's shirt and rather than hitting the couch during the wrestle, fell and hit the floor.

Maybir "immediately panicked" and ran to James to tell her of the boy's injuries but the mother said her son was "just faking it", Mr Brady told the court.

"He listened to Kayla James when she kept saying he was okay. He accepts he should have got the deceased medical attention," Mr Brady added.

The comments came after the crown said Maybir had given a number of versions of what happened to the boy after emergency services came to the studio on May 21, 2013.

The first was that the boy had fallen off a pogo stick and hit his head.

Then, months later he said the boy had actually fallen off a one-litre Nescafe coffee tin which he had got him to stand on as punishment for lying.

After the boy's death, the court heard, his body showed a litany of old injuries, including fractures to the ribs, left foot and a finger, and linear marks on his hands and buttocks.

The trial continues.