The death of 18-month-old twins in a Brisbane home has triggered calls for neighbours to be more aware of potential child neglect.

Police found the toddlers' decomposing bodies on Monday night in the cot they shared in a rented house in Sunnybank Hills, up to nine days after they died.

Their 30-year-old mother and 28-year-old father remain in custody ahead of an appearance in the Brisbane Magistrates Court on Thursday, charged with failing to provide the necessities of life.

Autopsies were being conducted on the twins on Wednesday, with the results expected to lead to an upgrading of the charges against the parents to manslaughter or murder.

Police on Wednesday said the charges had yet to be upgraded.

The twins' older sister, 11, and three older brothers, aged three, four and five, are now in the care of their grandmother.

She said the surviving children were healthy, but too young to understand what had happened to their brother and sister and why their parents were in jail.

"They are very traumatised," the grandmother, who cannot be named, told reporters.

She said her main aim now was to let the children know they were wanted.

"Just keep us as a family and show them a lot of love," she said.

"We are doing the best we can for them ... just to know that they are wanted and loved."

Asked how she was coping, she said: "As best as I can."

Teresa Scott, the president of the National Association for Prevention of Child Abuse and Neglect (NAPCAN), raised concerns over how the neglect of the two toddlers went unnoticed.

Neighbours have said at least one of the other children turned up on their doorstep looking for food, and some of them had been seen in the street during school hours.

"There are alarm bells that were there, there were warning signs," Ms Scott said.

"I'm not wanting to target these people, because we're all responsible.

"There are six kids in this family, somewhere along the line people must have had contact and seen them."

Queensland Education Minister Rod Welford said the parents had been contacted three or four times about their older children missing classes, but the school was unaware they were at risk.

"The school was aware there had been some attendance problems with these students, but not to an extent that would have alerted the school to any serious risk to the welfare or health of those children," Mr Welford said.

Queensland's Child Safety Department says the young twins were not known to them.

Acting Queensland Premier Paul Lucas called on residents to notify authorities if they notice children not receiving proper care.

"I think it's important whilst we all have an obligation that if we know something, then we say something," Mr Lucas said.

The suggestion was not about victimising or "pointing the finger" at people, he added.

Ms Scott said the community and governments ought to do more to prevent child neglect.

"These sorts of tragedies bring back to us that there were lots and lots of points somewhere along the line where if we had more prevention and health orientated services for the parent then perhaps this tragedy could have been averted," she said.