Family members identified the mother as Kellyanne Herman on Sunday.
It happened at Bustleton Avenue and Rennard Street in the city's Somerton section.
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Police say at around 8 p.m., a black Mercedes was speeding and appeared to have run a red light, hitting another car, which then crashed into a third vehicle.
The impact was so strong that the third car hit Herman and her child, killing her and leaving the boy in critical condition.
His family says he remains in the hospital on life support as of Sunday afternoon.
One of the cars involved in the collision was an Uber with a 77-year-old passenger inside.
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That senior was taken to the hospital and is expected to be okay.
As for the driver of the speeding Mercedes, police say he is 21 years old and alcohol does not appear to be a factor.