The boy, Kyrillos Gendy, was pronounced dead at Staten Island University Hospital, the police said.

The family, which lives in South Amboy, N.J., had just left the prayer meeting at the home of the children's uncle on Richmond Road, said Adam Gendy, 22, a cousin.

Just before he hit the family, at 8:25 p.m., the police said, the driver turned left out of the parking lot of the Diddle Dee Dairy and Deli at 1334 Richmond Road.

"Eyewitnesses say he did stop first, looked both ways," Mr. Gendy said, "and then hit all three of them in one shot."

The boy had severe internal bleeding and no pulse when he arrived at the hospital, Mr. Gendy added. "He wasn't breathing on his own," he said. "They managed to resuscitate him briefly."

Kyrillos's sister Gabriella, 7, sustained a broken ankle and his mother, Erieny Thomas, 35, had a gash on her face, Mr. Gendy said. Both were released from the hospital on Saturday afternoon. Mr. Gendy said the family had not yet told Gabriella what had happened. "That's a conversation we're trying to figure out," he said. "The mom is just an emotional wreck right now. She barely speaks."

After leaving the hospital, Ms. Thomas briefly went back to the house on Richmond Road. She walked with a limp and was helped up the steps by another woman. She paused briefly to look down at the street where the accident occurred. Her daughter had been taken elsewhere, a family friend said.

On Saturday afternoon, the police said, the driver, John Sanjurjo, turned himself in at the Hyland Boulevard station house. Mr. Sanjurjo, 33, who lives on Reno Avenue on Staten Island, was charged with one count of leaving the scene of an accident that resulted in a fatality, and two counts of leaving the scene of an accident that resulted in injury, the police said.

Mr. Gendy said he had seen Kyrillos just an hour before the accident. "He hugged me, gave me a kiss," Mr. Gendy said. "He's very innocent, very full of energy, very loving. Loved Marvel superheroes. Could name you all the superheroes."

He added that the boy's parents, who emigrated from Egypt before the boy was born, attend an Egyptian Coptic Orthodox church in New Jersey.

This article has been revised to reflect the following correction:

Correction: August 10, 2013

An earlier version of this article incorrectly stated the charges brought against John Sanjurjo. He was charged with one count of leaving the scene of an accident that resulted in a fatality and two counts of leaving the scene of an accident that resulted in injury, not two counts of leaving the scene of an accident.