The incident occurred at a six-story brick building on Oak Terrace just after 6 p.m. Friday.
Law enforcement sources told Eyewitness News that the victim fell out of a window at an apartment complex in Fort Lee.
The victim was rushed to Kings County Hospital, where he was pronounced dead.
Police responded to the rear of a building located at 301 West 114th Street around 7:15 p.m., where they found a child who tumbled about eight to 10 feet from the fire escape.
The 3-year-old girl was taken to Harlem Hospital with serious injuries.
The victim was taken to Maimonides Medical Center, where she is in stable condition.