An investigation was launched after Tyreece Scott was found with a stab wound in Grove Road on Tuesday morning.
The baby is safe and well in the care of hospital staff.
A member of the public out walking their dog called police at 21:13hrs on Thursday, 18 January after finding the baby girl in a shopping bag
The charge relates to an incident that is alleged to have taken place in November 2022 while the officer was off-duty