Tatiana Meakens, the mother, and Britany Meakens, the aunt, were both charged with several counts of child endangerment.
The fire started early on a Saturday morning in the West Englewood neighborhood. Officials say the home in the 6400-block of South Paulina was heated with space heaters and a hot plate, which sparked the fire at 3:35 a.m.
Javaris Meakens, 2, and Jariyah Meakens, 3, were killed. Two older siblings were able to escape.
Prosecutors said the women left the children alone in their West Englewood home while they attended separate parties.
"The older children in the back bedroom were able to get out of the apartment, but the younger children were trapped in the room where the fire started," said Assistant State's Attorney Jamie Dickler.
Prosecutors say the women had agreed that Tatiana would watch the children so that Britany could attend a party. But after receiving a phone call, Tatiana left for another party.
"She ran out of the house even though Britany told her not to go. When Tatiana left, she told Britany she was leaving, despite what had been agreed to earlier," said Dickler.
Prosecutors say Tatiana returned home after several hours, only after she was told the apartment was on fire.
"The mother left when there was somebody taking care of their children. The aunt actually thought the mother was coming right back," said Marijane Placek, public defender.
Placek says heat was cut off at the apartment and the women were doing the best they could to keep it warm.
Placek also also said there were no working smoke detectors in the apartment. She believes the landlord should share some of the blame.
"Why didn't he do something? Why weren't there any smoke detectors?" Placek said.
Meanwhile, the landlord says People's Gas is responsible for turning the heat on or off. He says he advised his tenants to find temporary housing to keep warm until things were cleared up with the gas company. He added that he maintains working smoke detectors.
Britany Meakens, 22, pleaded guilty to two felony counts of child endangerment and was sentenced to five years in prison by Judge Diane Cannon, according to Cook County State's Attorney's office spokeswoman Tandra Simonton.
Autopsies determined both children died from carbon-monoxide intoxication and inhalation of smoke and soot, the Cook County Medical Examiner's office said.
Firefighters arrived to find flames shooting from a side bedroom window on the first floor of the building, where Javaris and Jariyah were trapped, authorities said. Crews sawed off the bars from a basement window trying to rescue the children, but it was too late.
Two other boys — Darnell, 7, and Marquis, 4 — were rescued from the burning building by a relative and were taken into the custody of DCFS.
Tatiana Meakens, 23, is due back in court Aug. 1. She has pleaded not guilty to two felony counts of child endangerment and two misdemeanor counts of endangering the health of a child.
She remains in the Cook County Jail, where both sisters have been held since their arrests on $100,000 bonds.
The Sun-Times Media Wire contributed to this report.