"We are surprised about [the child's death] because we thought all this was over when they arrested that man but it's still continuing," the toddlers' grandmother Vinah Mali said in Xhosa on Monday.

The family of Diepsloot toddlers Yonelisa and Zandile Mali killed last month have expressed shock over the death of a baby in the same area.

"We are surprised about [the child's death] because we thought all this was over when they arrested that man but it's still continuing," the toddlers' grandmother Vinah Mali said in Xhosa on Monday.

The seven-month-old baby's mutilated body was found in a shack in the area, north of Johannesburg, on Sunday.

The baby's mother reported the death to the police early on Sunday morning, claiming rats attacked her child. When police arrived on the scene, the woman had disappeared. Pathology tests apparently confirmed that rats attacked the child.

But, police spokesman Captain Tsekiso Mofokeng said a case of murder was being investigated.

"We have registered a case of murder, but initially it was an inquest," Mofokeng said.

Police arrived to find the baby's body with a foot missing.

"Further investigations informed police that [the foot] was bitten off by rats."

Police were still awaiting the results of the post mortem to definitively determine the cause of death. Mofokeng said the baby's mother was missing and had still not been located by Monday morning, contrary to media reports.

Mali said the prayer day organised for the people of Diepsloot helped the family.

"We feel better. At first we were not at peace but since we got the prayers we feel better. Our spirits are still low because there are fewer of us in the house," she said.

Women, Children and People with Disabilities Minister Lulu Xingwana urged the religious leaders present at the Methodist Church to pray for the country.

"We all know that this scourge is traversing the entire country. There is not one province that has been saved," she said.

"We need divine intervention in our country to ensure that we exorcise the devil, whether it is in the form of drugs, rape against women and children, or bullying.

"Nobody has the right to violate those innocent angels," she said, looking at the children accompanying the Mali and Mkondo families.

In September, five-year-old girl Anelisa Mkondo was found dead in the same area. Yonelisa and Zandile Mali, aged two and three, were found dead in a toilet cubicle in Diepsloot's extension one in October.

"In the past few weeks we've seen children being abused, poisoned, neglected, murdered, raped, trafficked, and used for pornography. Something, somewhere has gone wrong in the fabric of society."

Johannesburg mayor Parks Tau said it was up to people to take responsibility for what happened and to hold public servants accountable if they failed to do their jobs.

"We have the responsibility in our communities to stand up and say 'What can I do to make my community better?' The ghastly experiences are a reflection on us as a people... who kill their children. A people who rape and murder their children, who do not care about the value of the lives of our women and children," Tau said.

He urged people to work together with law enforcement agencies and government in targeting crime and known criminals in their areas.

Religious leaders joined Xingwana and Tau on Monday to pray for Diepsloot.

Following the murder of the Mali cousins, Diepsloot residents stoned cars and burnt tyres in the street outside the local police station in protest.

A 29-year-old man faces charges of murder, rape, and kidnapping in connection with the cousins' deaths.

National Prosecuting Authority spokesman Medupi Simasiku said police were still investigating Mkondo's case.