It happened around 5:15 p.m. on the 5000 block of Rising Sun Avenue in the city's Olney section.
Police said there was some type of argument before a man fired his weapon.
At the time of the gunfire, there were several children inside the barbershop getting haircuts ahead of the first day of school Monday.
"Tomorrow is the first day of school, many parents were bringing their kids in for haircuts," Philadelphia Police Inspector D.F. Pace said. "One of the mothers was so traumatized she said there's no way her children are going to be able to go to school tomorrow given what they just experienced."
Police say a 4-year-old boy, who was inside the business with his father, suffered a gunshot wound to the shoulder.
The father tried to rush the child to the hospital but police say he crashed the car at 13th and Grange Avenue in the city's Fern Rock neighborhood. The driver of the other vehicle then jumped into action and took the boy to the hospital where he was placed in stable condition, police said.
"That gentleman took the kids and put (them) in the white car and then they all drove off," recalled Rasheeta Patterson, who witnessed the crash.
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No other serious injuries were reported in the shooting and crash.
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Police are still searching for the suspect.
Anyone with information is asked to call police at 215-686-TIPS.