ROSALIND PORTER was a nurse for 15 years, a frequent witness to death and heartbreak.

But nothing could prepare her for what she saw yesterday a few feet from her front door on 57th Street near Litchfield in Kingsessing:

A 4-year-old boy lay on the pavement, broken and bleeding. A ninja-like action figure, clad in black, lay just beyond the hand that had been clutching it moments earlier.

Porter, 60, didn't know it at the time, but those were the boy's final moments, on a night on which another child was critically hurt, alongside his mother, at the hands of a different careless driver in another part of the city.

"I want her to turn herself in," Porter said of the driver who had hit the 4-year-old with her black SUV about 6:30 p.m. and kept going.

"This right here," the retired nurse said, gesturing at the police cruisers, whose dome lights were bathing her stoop in blue-and-red, "this is the worst thing I've ever seen."

Surveillance footage of the incident, viewed by the Daily News, is horrific:

The boy can be see darting onto 57th Street from between two parked cars. A black SUV hits the child, sending him flying forward onto the pavement.

Then, without slowing, the vehicle drives over the boy before speeding away.

Porter said her neighbor, whom she identified only as Linda, had just parked on Warrington Avenue when the boy landed alongside her car door. Linda got out and started to scream for passersby to chase the SUV, Porter said.

It was too late: The woman behind the wheel was long gone.

A small crowd started to form, including the boy's mother, who ran screaming into the street from her home on Litchfield, according to witnesses.

About that time, Raysa Cespedes stepped out of her brother-in-law's nearby corner store to see what had happened. She saw the boy's mother, hysterical, drop to her knees. She was screaming, pleading, " 'Please don't let him be dead,' " said Cespedes, 18.

Soon medics arrived. They tried to revive the boy, but were unsuccessful. Cespedes watched as they loaded him into the ambulance and sped off toward Children's Hospital of Philadelphia.

He was pronounced dead there about 7 p.m., according to police.

As doctors delivered that grim news, another, similar incident was unfolding in North Philly.

A 19-year-old woman was crossing Mascher Street near Lehigh Avenue, carrying her 2-year-old son in his car seat, Chief Inspector Scott Small said.

She was feet from her door when a white sedan, either an Infiniti or Nissan, carrying two men, slammed into her. The sedan never slowed, turning onto Lehigh before fading from view.

Last night, the woman was in critical condition at Temple University Hospital with severe head trauma, Small said.

Her son was at St. Christopher's Hospital for Children with a broken pelvis, two broken legs and severe head trauma. He was in "very critical condition," Small said.

Back on Warrington, distraught neighbors gathered around the scene of the crime, expressing sadness and outrage.

Porter was in tears. The street is "like a highway," she said.

Usually, weather permitting, Porter and her other neighbors sit on their porches, hollering at the neighborhood kids when they get too careless around the passing cars.

"But we weren't out there today," she said, her voice trailing.

Investigators last night were still searching for both vehicles, police said.

Tipsters should call 215-686-8477.