Queensland police have laid more charges against the mother of fatally injured toddler Mason Jet Lee and her former partner.

Anne Maree Lee, 27, and William Andrew O'Sullivan, 36, will appear in Caboolture Magistrates Court on February 6 charged with one count each of cruelty to children.

Police will allege the pair, who are already in custody charged with manslaughter, failed to provide adequate medical assistance to the 22-month-old between December 23, 2015 and February 13, 2016.

Mason died at a Caboolture home, north of Brisbane, in June 2016 as the result of inflammation from a ruptured small intestine. At the time of his death he had injuries from head to toe after being released from hospital just three months earlier.

Advertisement

A third person, Ryan Robert Barry Hodson, who also lived at the home where Mason died, is also charged with the toddler's manslaughter and was released on bail in August.

The ABC reports that Mason had been vomiting for five days before his death and had widespread bruising.

Police alleged he had suffered traumatic injuries in the day before his death and ultimately died of peritonitis.

Peritonitis is usually the result of a fungal or bacterial infection caused by an abdominal injury or an underlying medical condition.

At the time, Child Safety Minister Shannon Fentiman said another nine employees were the subject of disciplinary proceedings.

Ms Fentiman said the Systems and Practice Review into the Department of Child Safety's interactions with Mason and his family found that "staff may have breached legislation, standards, codes and procedures in this case and consequently 12 safety workers have been to the Department's Ethical Standards branch."

Opposition child safety spokeswoman Ros Bates said more than 50 children known to Queensland's child safety department died in 2016.

"It's obvious the child safety department is in crisis and it is failing in its primary role of keeping children safe," Ms Bates told ABC radio. "We have had over the past 12 months 51 deaths known to child safety, of those there are at least eight children who have died under terrible circumstances and another 16 which are being investigated."

- With AAP

In November last year three staff members from the Queensland child safety department were stood down after an internal review into Mason's death.