The child was among 13 people shot in Cornell Square Park on the city's South Side late Thursday night. None of the other victims were listed in critical condition early Friday.
The January shooting death of another child, 15-year-old Hadiya Pendleton, brought national attention to Chicago because the band majorette had performed in Washington at events surrounding President Barack Obama's inauguration in January.
The president invited Pendleton's parents to his State of the Union speech in February. Obama mentioned her in that speech and a few days later when he returned to Chicago, his hometown, for another speech in which he pressed for stricter gun laws.
Police charged two men in Pendleton's death. They said the two were gang members seeking revenge and mistook Pendleton for someone else.
Investigators believe Thursday night's shooting was also gang-related, said Officer Ron Gaines of the Chicago Police Department.
The 3-year-old victim was shot in the ear, and the bullet exited through his mouth, said Officer Ron Gaines of the Chicago Police Department.
The other victims included two 15-year-olds who were listed in stable condition, Gaines said. The remainder were adults ages 21 to 41. Four were in serious condition. The conditions of the others were listed as stable or good. One adult was treated and released from a hospital.
The shooting occurred in Cornell Square Park. Video from CNN affiliate WLS-TV showed police had taped off an outdoor basketball court.
No suspects were in custody late Thursday.
The FBI's annual crime report this week showed Chicago had 500 homicides in 2012, up from 431 in 2011 and more than any other American city. Chicago officials have said homicides this year are below the 2012 pace.