Police are now trying to track down the person or people who assaulted that driver.
It happened around 4 p.m. Wednesday on Oregon Avenue near 9th Street.
"It was horrific to see the child underneath that truck the way he was. I just pray for him and his family," said Mike Graham, who witnessed the incident.
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Surveillance video shows the seconds before the crash. The bicyclist veers in front of a black truck and that's when the boy is hit.
The child was dragged for a block from 9th and Oregon to Darien Street.
Police say the 12-year-old boy was rushed to Children's Hospital of Philadelphia after the crash. He's currently listed in stable condition.
Witnesses told police the driver got out of his truck and tried to take off running but he did not get far.
Investigators say the driver was beaten by a bystander or bystanders who stopped him.
"Tempers were flaring and people were thinking 'this was a child, and this guy was trying to get away with, God forbid, murdering him,'" said Graham.
The Accident Investigation Division is working along with South Detectives to collect additional video and statements and to track down the person or people who beat up the driver before police arrived.
The driver, who is facing DUI charges, was also hospitalized. He has not been identified at this time.
The boy who was hit is expected to survive his injuries.