Chicago Fire Department officials said the child and two other victims are in a critical condition.
The shooting occurred shortly after 10pm last night in a park in the city's Back of the Yards neighbourhood, with at least 10 ambulances rushing to the scene.
One witness, Julian Harris, said dreadlocked men shot at him from a grey car before turning towards Cornell Square Park and firing at people in the area. His three-year-old nephew was wounded in the cheek.
"They hit the light pole next to me, but I ducked down and ran into the house," he said. "They've been coming round here looking for people to shoot every night, just gang-banging stuff. It's what they do."
Authorities said no-one had been taken into custody in connection with the shooting.
Chicago police have responded to recent shootings that have grabbed national headlines by stepping up patrols in certain areas, including the Back of the Yards.