Police found the bodies of the twin boy and girl at a house in Sunnybank Hills, in Brisbane's south, around 7pm (AEST) on Monday.
Post-mortem examinations were to be carried out on the children on Tuesday.
It is understood three older siblings have been taken away by child safety workers to another residence.
A 28-year-old man and a 30-year-old woman were to appear in Brisbane Magistrates Court on Tuesday, charged with failing to provide the necessities of life.
Neighbour Nyakong Maying told AAP she had lived in the same street as the family for five years and sometimes gave food to the children in the family.
"The youngest boy (a four-year-old boy) comes over here and says `I need something to eat, I'm hungry'," Ms Maying 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."
Ms Maying, who came to Australia from Sudan, said she never saw the parents.
"I never see the mother or the father also, I just see the kids because they come around my house," she said.Another neighbour, Fiona Ma (Ma), said she had noticed a boy aged three or four who was allowed to run around the neighbourhood unsupervised.
"I feel confused because (the) parents are not attending to him," Ms Ma told AAP.
"He's so young and he just runs in the street."
--I hope the parents go to jail! What a horrible thing to do.