Police say 29-year old Yancy Arevalo was walking eastbound across Route 110 just south of Nathalie Avenue, pushing a stroller with her 10-month-old daughter, Britney Arevalo, inside when they were struck by a 1998 Chevrolet pickup truck heading north on Route 110 at about 7:00 p.m.
Arevalo and her child were taken to Good Samaritan Hospital Medical Center in West Islip where the infant died from her injuries early Sunday morning.
Arevalo suffered only minor injuries, but she is being held for observation because she is pregnant.
The driver of the pickup, Arthur Plowden, 46, of North Amityville was not injured. His vehicle was impounded for safety checks.
The investigation is continuing.