(CNN) -- A mass shooting at a Chicago park left a 3-year-old boy in critical condition and returned the spotlight to gun violence in the city with the nation's highest number of homicides.
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 was listed in critical condition early Friday.
The shooting prompted Mayor Rahm Emanuel to cancel a trip to Washington.
"Senseless and brazen acts of violence have no place in Chicago and betray all that we stand for," the mayor's office said in a statement. "The perpetrators of this crime will be brought to justice and prosecuted to the full extent of the law. I encourage everyone in the community to step forward with any information and everyone in Chicago to continue their individual efforts to build stronger communities where violence has no place."
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, he said.
The other victims included two 15-year-olds who were listed in stable condition, Gaines said. The rest 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 at a hospital and released.
Video from CNN affiliate WLS-TV showed police had taped off an outdoor basketball court at Cornell Square Park.
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.