How could toddlers starve to death in suburbia?

IN A home so ordinary it could be on Ramsay Street, twin toddlers have starved to death, left in their cot until a sibling noticed the smell.

Lily Rose and Zadie Vincent Matthews-Jackman lived for just 18 months, at the end of which one weighed four kilograms, the other a little less. Many newborns weigh more.

When their eldest sibling found them dead on Monday, the 11-year-old told their mother: "I know why you've been crying now."

They lay dead for more than a week, in a middle-class house in a middle-class suburb, Sunnybank Hills, in southern Brisbane. They were decomposing as their parents - Kylie Maree Matthews, 30, and Mark Ryan Jackman, 28 - went about their daily lives.

Police arrived about 7pm on Monday, and late yesterday morning the pair faced a Brisbane court, charged with failing to provide their twins with the necessities of life.

Police expect to lay either murder or manslaughter charges this week after post-mortem examinations, although they suspect malnutrition was the cause of death.

The Department of Child Safety said last night the twins were not known to it. Although it investigated an incident involving the family some years ago, it said no evidence was found to justify an intervention.

Matthews appeared in the dock first, barefoot and wearing a brown prison tracksuit. The mother of six was teary at first, before composing herself and staring at the floor.

She did not look up when the police prosecutor, Michelle Clarke, told the court she had replied to the obvious police question - how did they die? - with the words: "I don't think I fed them enough."

She did not look up when the court was told she rarely changed their nappies, that they rarely left their bedroom, or that their siblings rarely saw them.

She did not look up when it heard she had noticed her twins were dead one morning on the June long weekend - either Sunday or Monday - but left their bodies to decay in their cot.

It heard she had a cold, it heard of relationship difficulties between her and Jackman, who sat impassively in the dock after her, but it heard nothing to properly explain why Lily and Zaide were left to die.

Jackman's lawyer, Michael Cridland, said the roadwork project manager had little contact with the twins in the past six months and discovered their deaths only on Monday.

But a police prosecutor, Tina Green, said Jackman lived in the same home and had to walk past the toddlers' bedroom to reach his own.

The magistrate, Noel Nunan, remanded both in custody until tomorrow, when a contested bail hearing is expected after Matthews has a psychiatric evaluation (Jackman has refused one).

Mr Nunan said the circumstances were "bizarre". Similarly troubled were neighbours in the commuter suburb.

Like most of them, Fiona Ma did not know the twins existed. She recalls one of the other children, a boy about four, who appeared healthy but unsupervised.

Another neighbour, who did not wish to be named, said the family moved into their rented home at Christmas - about the time Jackman says he last saw the twins.

The neighbour heard Matthews swearing at her children but said occasional screaming did not appear out of the ordinary. "We didn't even know there were twins," he said. "No one realised." He said he last saw Matthews on Thursday and she did not appear distressed.

Another neighbour, Nyakong Maying, told AAP she sometimes gave food to the four-year-old. "The youngest boy comes over here and says 'I need something to eat, I'm hungry'," she said. "When they came here about four months ago, I give them some snacks or fruit with my children, but after that I stopped it."

The four other children are being cared for by Matthews's mother