A Chicago grandmother pleads for a respite as the television cameras roll: "Y'all out here killing these innocent people, kids, parents, grandparents, mothers, fathers: It's got to stop. You need to stop."

Semehca Nunn's grandson was in the hospital after being shot in the head Thursday night. In all 13 people were shot at a park in the city's South Side.

Except for the boy, Deonta Howard, none of the other victims were listed in critical condition, but that fact offered little relief.

Once again, Chicago is in the spotlight over gun violence; a reminder that it is the city with the highest number of homicides in the country.

The violence "needs to stop," said a tearful Nunn said, after she came home to find police and television cameras all around. It was only then that she learned her grandson had been shot in the ear, and that the bullet exited through his mouth.

Deonta's condition has stabilized and he is heavily sedated and will have plastic surgery on his face, Nunn said.

"They said he is going to be OK," she said. "That's what Grandma gave him, strong man, 3 years old, strong survivor."

The other victims include two 15-year-olds who were listed in stable condition, said Officer Ron Gaines of the Chicago Police Department. 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 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."

Investigators believe Thursday night's shooting was gang-related, Gaines said.

"It's pretty frustrating, it's very disappointing this is happening in our neighborhood once again," said the Rev. Corey Brooks, a spokesman for the 3-year-old's family.

On any given day, any child in the park or walking to school can be shot, until the community does something about it, he said.

"The truth is that in Chicago, we are facing murders every single day on the south side and west side," Brooks said. "Blacks and Latinos are facing extreme violence."

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 address 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.

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.

Chicago bans some semi-automatic weapons and high-capacity magazines, and restricts handguns.

CNN's Kara Devlin, Shawn Nottingham, Tina Burnside and Jennifer Feldman contributed to this report.