Fire Department spokesman Larry Langford said firefighters arrived on the scene several minutes after the fire broke out on the third floor of an apartment building in the Rogers Park neighborhood, the Chicago Tribune reported.
Langford said seven children went into cardiac arrest after being pulled from the building and efforts to revive five of them failed. Two children and an adult woman were taken to area hospitals, where the sixth child later died.
Investigators were checking a report that a third floor apartment had no electricity and the family living there used candles to see in the dark.
"We've been told they were using candles," Langford said. "We don't know for sure."