The motive behind the act is that she did not have food to feed the child.
Police have since detained the woman.
In a statement, police spokesperson Rae Hamoonga said Mokwane Maeke 27 of unmarked house in Kamwala South area reported that her younger sister Mosowe Maeke 22 murdered her child Sangwani Chabinga by pressing a pilow on him and died of suffocation.
He said the incident on August 13 between 17:00 and 19:00 hours at a named Lodge in Kamwala South.
