Child safety officers and police were warned toddler Mason Jet Lee was in danger of being physically harmed months before he died.
The 21-month-year-old was struck in the abdomen by his mother's boyfriend, William O'Sullivan, in June 2016 and died from sepsis.
Children, who cannot be identified for legal reasons, told officers in March 2016 that O'Sullivan was hanging around "all the time".
They also raised concerns for Mason, saying they would save him if he got hurt, the Brisbane Coroners Court heard on Tuesday.
"Smacking him ... a bad guy," counsel assisting Jacoba Brasch QC said reading a transcript of children's answers to interviewers' questions.
"Like really bad ... punched."
"Because if it does happen he might die."
A Mission Australia social worker, who also cannot be named, said she became concerned about O'Sullivan after he responded defensively about the Lee family being interviewed by child safety officers.
"For me it was quite obvious he was worried about what (they) might say," she said from the witness box.
The woman said when she began working with Mason's mother, Anne-Maree Lee, the family was homeless and struggling.
The court heard Ms Lee had been known to child safety officers since 2005, following numerous domestic violence incidents involving drugs.
By November 2015, the child safety department's concerns about Ms Lee had increased to include her ongoing mental health issues and alcohol abuse.
She was also allegedly selling drugs from the home she shared with her children and police had been called to a domestic violence incident involving O'Sullivan.
But none of this was communicated to the social worker tasked with providing early intervention support services to the family.
"That's really concerning information. It would have helped me to have a much better idea of the family's history," she said.
The silence continued when Mason was hospitalised in February 2016 with injuries his veteran doctor described as the worst he had seen in his 45-year career.
It was only after pediatricians raised their concerns about Mason and his case was escalated to a Suspected Child Abuse and Neglect team in March 2016 that the social worker learned about the Lee family's broader problems.
"I was alerted to how severe the issues were," she said.
The social worker said doctors at the meeting advocated for Mason to be removed from his mother and O'Sullivan's care.
Despite this, Mason was released from hospital to them after child safety officers agreed to begin an intervention process.
However, Mason died three months later on June 11 before the child safety department allocated Mason's case to an officer.
Earlier, the inquest heard Mason suffered a severe skin condition, a fractured leg and a bacterial infection causing his right leg to swell to twice its normal size in the months before he died.
A doctor also observed a tear to Mason's anus, which was suspected to have been caused by sexual abuse.
The inquest will now continue via written submissions and answers only due to the threat posed by the coronavirus.