Five other preschool-age children and one adult escaped unharmed, fire officials said.

The fire, which began shortly after 10 a.m. Wednesday, left the house at 8424 S. Saginaw Ave. with extensive damage, according to Chicago Fire Department spokesman Larry Langford.

Langford said a firefighter using a thermal imaging camera found the sixth child in the closet of a rear bedroom on the first floor and carried him outside.

The boy was transported to Advocate Trinity Hospital in extremely critical condition and pronounced dead shortly afterward.

Two engines and two trucks responded to the original call. Additional units were later called to the scene and had the fire under control "within minutes," Langford said.

One truck was involved in a minor accident with a car at 83rd Street and Yates Avenue while responding to the fire, but no injuries resulted, and it did not affect response time, said Langford.

The cause of the fire is still under investigation.