Queensland mother Anne Maree Lee has been sentenced to nine years in jail after today pleading guilty to child cruelty and the manslaughter of her toddler Mason Jet Lee.

Key points: 22-month-old Mason died in 2016, days after a blow from his stepfather

22-month-old Mason died in 2016, days after a blow from his stepfather His mother failed to seek medical help despite obvious signs he was in pain

His mother failed to seek medical help despite obvious signs he was in pain Crown prosecutor Michael Byrne described the last days of Mason's life as a "wretched existence"

However the 29-year-old will be eligible for parole from July this year, given the two years and seven months already served.

Attorney-General Yvette D'Ath is seeking advice from the Office of the Director of Public Prosecutions as to whether there would be grounds for a legal appeal against the sentence.

"Mason Jet Lee's death was a tragedy that Queenslanders everywhere have felt," she said.

Lee sobbed when she was arraigned in the Supreme Court in Brisbane this morning, with her lawyer saying she had profound guilt and grief over the death of the 21-month-old.

She had also admitted to cruelty for neglecting Mason's injuries to his leg and anus in the months before his death.

Lee will be eligible for parole after a third of her nine-year sentence is served. ( ABC News )

Mason died in June 2016, days after being punched in the abdomen by his stepfather and Lee's then-partner William Andrew O'Sullivan.

Crown prosecutor Michael Byrne said that while O'Sullivan inflicted the fatal blow at his Caboolture home, north of Brisbane, Lee did not take her son to a doctor.

Mason would have been in severe pain before his death, suffering from multiple injuries, including a perforated bowel, the court heard.

Mr Byrne described the last days of Mason's life as a "wretched existence".

"He was vulnerable and defenceless and the one person he was entitled to receive shelter [from] ... not only failed to do that, but in reality contributed [to it]," he said.

"This is not a momentary or short-term failure to act, or a single decision not do something in the best interests of the child.

"Had medical treatment been provided, the condition was survivable."

"It would have been obvious to any person that he was very sick and in urgent need of medical attention."

O'Sullivan is serving a nine-year sentence over Mason's death. ( ABC News )

Defence counsel Tim Ryan told the court his client had a "profound sense of grief and guilt" for failing to protect her son.

"Regardless of the sentence, she will have to live with that fact for the rest of her life," Mr Ryan said.

He said Lee was not aware of the life-threatening injuries inflicted by O'Sullivan, who has already been sentenced to nine years in jail, but agreed she neglected to get help for the toddler.

In sentencing, Justice Jean Dalton said she allowed her child to live with O'Sullivan who was violent and a known drug user.

"The child must have been in dreadful pain," he said.

"It's not suggested you had any part in delivering the blows ... it's not suggested that you knew that injury had been inflicted.

"The case against you is on the basis of neglect."

Traces of drugs found in Mason

The court heard an autopsy revealed Mason had traces of methylamphetamine in his system but there was no suggestion he was given the drug on purpose by either Lee or O'Sullivan.

Mr Byrne said it is most likely Mason touched a surface the drug had been on.

Mason had been hospitalised with injuries the same year he died. ( ABC TV News )

Lee knew that O'Sullivan was prone to "extreme anger" when he used ice but still left her son in her former partner's care, the court heard.

She had met with a representative from the Department of Child Safety the week Mason died but never mentioned any concerns for her son.

"She wanted a plan to get out of the relationship," Mr Byrne said.

"[Lee] explained O'Sullivan was extremely violent when he used ice."

The court earlier heard that in the year that Mason died, he was taken to hospital with serious unexplained injuries, including to his leg and anus.

"At the time of his admission to hospital the pain was said to be so severe it required a narcotic infusion," Mr Byrne said.

"He had … mouth ulcers and infected skin lesions — more commonly found in children who receive a low standard of care."

A third person, Ryan Robert Barry Hodson, who also lived at the home where Mason died, was also charged with the toddler's manslaughter, but the charges were dropped.