Cook County Asst. State's Attorney Jennifer Dillman said Chambers fired into Cooper Park, hitting the child and two others. Chambers is a member of a rival gang which says Cooper Park is its turf.
Dillman said the boy was struck in the abdomen, kidney, and legs and remains in critical condition Sunday.
Court records show Chambers has a prior weapon-related conviction and was on YouTube "espousing the virtues of gang membership.''
Police said Chambers was "positively identified as the individual who shot a 5-year-old male" at the park, at 117th and Ada streets, shortly after midnight July 5.
The shooting stemmed from a conflict between two rival gangs, according to law enforcement sources. Last July, two girls ages 10 and 12, had been shot near Cooper Parkin another incident with strong gang overtones.
The boy was the most seriously wounded of the three people shot. He was transferred to Advocate Christ Medical Center in critical condition after someone drove him and the other two men wounded to Metro South Medical Center. The two wounded men are 28 and 34.
Tribune reporters Jeremy Gorner and Rosemary Regina Sobol contributed.