Police said the crash happened in the McKinley Park neighborhood's 3500 block of South Ashland Avenue just after 4:30 p.m.
A 43-year-old woman was driving a sedan northbound on Ashland Avenue. She tried to turn left onto 35th Street when a 16-year-old boy, who was driving an SUV southbound on Ashland Avenue, struck the passenger side of her sedan.
Police said a 3-year-old boy, who was in the sedan, suffered a head injury and was transported to Stroger Hospital in critical condition. Another passenger in the sedan, a 42-year-old man, was taken to the same hospital with minor injuries. The sedan's driver was not injured.
The teen driver was taken into custody, but no citations have been issued, police said.
The Major Accidents Unit is investigating. Police did not immediately provide further information about the crash.