He was covered in bruises because of a medical condition which led to him having issues with spatial awareness.

But the condition also masked violent, irrational and unjustified attempts at discipline from his aunt and foster mother Jodie Maree Powell.

They included banging his head against a wall, throwing a knife at his leg and striking Curtis with a carving fork, power cord and belt.

It was a fear of exposing these signs of abuse that stopped Powell, a nurse, from getting Curtis the medical help he needed before he died of bronchopneumonia on July 15, 2015.

He would have appeared to be very unwell and had difficulty breathing in the days before his death.

"Curtis relied on you to care for him as his parent and you failed him," Supreme Court Justice Burns said in sentencing Powell in Brisbane on Wednesday.

Powell had pleaded guilty to manslaughter and assault occasioning bodily harm at a court hearing earlier this year.

She was sentenced to nine years' imprisonment with a parole eligibility date of June 14, 2020.

Curtis had been living with his aunt since he was three because his mother had drug issues.

Outside court, Curtis' father Dallas Bolton says he thinks about his son every day.

"The main thing I asked (Powell) to do was to look after Curtis as if he was her own and she failed miserably," Mr Bolton said.

"Not a day that goes by that I don't think of him and I don't shed a tear."

Curtis' mother Kristie Anne Powell said she missed her son.

"I'm in shock still. That was my sister. That was someone I grew up with my whole younger life," Ms Powell said.

"To believe someone could hurt a child so much, especially a family member, is unforgivable in so many ways."

"I am happy with the outcome and I hope it will deter such a thing from happening again."

Australian Associated Press