The shooting happened just after 2 p.m. on the 700 block of E. Locust Avenue in the city's Germantown section.
When officers arrived they found two men suffering from gunshot wounds. Nearby, police say a 12-year-old boy was found shot just a short distance from the men.
All three victims were taken to an area hospital where they died.
The child was identified as 12-year-old Laron Williams, who lived on E. Locust Avenue.
The shooting also claimed the life of 30-year-old Khalif Chambers, of Philadelphia, and 47-year-old Riley Darden of Norristown.
At least 12 shots were fired at the scene, according to police.
Philly police provide update on deadly triple shooting
"We know that the two adult males were hit right at the top of the block, right by Crowson (Street), where they were found by police. It appears the juvenile was able to run towards his residence and was found a short distance away from the adults," said Deputy Commissioner of Investigations Frank Vanore.
Police believe the shooters were driven to the scene and left in the same vehicle. Investigators are reviewing video to develop a description of the suspects.
As for the young victim, sources tell Action News Williams was celebrating a birthday Thursday.
He is now among at least 154 victims in the same age group who have been shot so far this year, including 27 who were shot and killed.
"Devastated to learn of the tragic killing of three people, including a 12-year-old child. No one should have their life and potential cut short by violence. Our communities deserve better. This senseless violence must stop," said Mayor Jim Kenney in a statement on Twitter.
Further details on what led up to the shooting were not immediately available.
Anyone with information is asked to call police at 215-686-TIPS.
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