Christen Dale, 21, was arrested Thursday for beating Ethan Ali inside their family's home at 287 Rockaway Parkway the day before, according to the NYPD.
Emergency workers found Ethan covered in bruises, unconscious and unresponsive about 1:30 p.m., police said.
He was pronounced dead at the scene, police said.
The medical examiner determined that Ethan was killed by multiple blunt impact traumas and ruled his death a homicide, a spokeswoman said Thursday.
Dale was arrested on charges of manslaughter, assault, endangering the welfare of a child and criminal possession of a weapon, police said.
She was still awaiting arraignment on those charges Friday morning, records show.
Ricky Rivera, 21, a next door neighbor who is friends with the boy's father, said that he frequently saw Ethan playing outside during the summer.
"He was playful, a healthy kid," Rivera said. "Always smiling."