Investigators are trying to figure out where the parents were at the time.
Thursday, investigators had determined the fire broke out Wednesday afternoon near the basement stairs of a home in the 3100-block of Concord Lane, but they were still unclear as to how.
Waukegan area fire officials were called to the Tidy Midlane Club subdivision just before 4:30 p.m. and encountered a house engulfed in smoke with two children inside.
"We were met with heavy smoke and the doors were looked and we could hear some children screaming inside," said Chief Dan Young, Waukegan Fire Department.
The children were brought out in varying degrees of consciousness. A next door neighbor called 911 after a frantic neighbor pounded on his door.
"We started panicking so I end up calling the fire department. And I run over to the window window and I'm yelling up there, saying 'who's up there,' and I hear this kid yelling and he's screaming that he can't breathe," said Terry Dejaresco, neighbor.
Fire officials say there was no adult at home and the girl and boy likely started the fire in the basement. The smoke drove the kids upstairs
"They were just screaming, 'help, I can't breathe, I can't breathe, we're going to die,'" said Dejaresco.
The mother of the children is with them at Loyola Hospital in Maywood. She told another neighbor she is "thankful to God her kids didn't perish in this tragedy and they're getting care now." That person told ABC7 the mother has another 5-year-old child who is staying with that neighbor down the street.