Police Superintendent Gary McCarthy said Friday it was a "miracle" no one died in what investigators said was likely a gang-related incident late Thursday in Cornell Square Park in the Back of the Yards neighborhood.
McCarthy told a news conference suspected gang members pulled up in a car and opened fire on a basketball court with a military assault-style weapon.
The 13 park injuries were among two dozen citywide, four of them fatal, police said.
McCarthy said urban violence is fueled by illegal weapons and "reasonable gun control laws" should be enacted on the federal and state levels to curb the carnage.
Among the actions McCarthy recommended is requiring transfers of weapons among individuals to be reported to authorities to eliminate straw purchasers. He said military-style weapons with high-capacity magazines, like the ones used in Thursday's shootings, have no place on the street.
McCarthy pledged to bring the shooters to justice.
"We are bringing the full force of this department ... and law enforcement partners ... to come to a quick conclusion," he said, adding though a number of the victims were gang members, it was unclear who the intended target was.
Mayor Rahm Emanuel canceled an East Coast trip and returned to Chicago in the wake of the violence.
Chicago had more than 500 homicides in 2012.
Police said the 3-year-old was in critical condition Friday from a wound caused by a bullet entering his head at an ear and exiting through his mouth, the Chicago Tribune reported.
"They hit the light pole next to me but I ducked down and ran into the house," said Julian Harris, 22, uncle of the 3-year-old who was shot. "They've been coming round here looking for people to shoot every night -- just gang-banging stuff. It's what they do."
Harris said gunmen in a gray sedan fired at him on a corner before heading to the park, the Chicago Sun-Times said. Other witnesses said two gunman exited the car and began shooting.
At one point, about 60 police officers were at the scene, the Tribune said. At least 10 ambulances responded.