Chicago fire officials say the boy suffered significant burns and was taken to a hospital in critical condition.
The fire broke out around 6:35 p.m. Saturday near 68th Street and South Merrill Avenue in the city's South Shore neighborhood.
Two adults were also hurt, officials said. A 29-year-old man was also in critical condition, and a 26-year-old woman was expected to be okay.
Fire investigators believe the fire was accidental.
No further information was available.