The three-year-old is fighting for her life at a local hospital where she was admitted after the incident.
Priscilla Chidamba (27) and her son Innocent Mujeye (7) died on the spot.
The incident has left the Glen Norah community in shock.
National police spokesperson Assistant Commissioner Paul Nyati confirmed the incident.
He said that the police were still investigating the circumstances that led to the tragedy.
“The police are investigating circumstances surrounding an incident in which Priscilla Chidamba and her son, Innocent Mujeye (7) died after allegedly consuming a poisonous substance,” he said.
Reports claim that on Wednesday, Priscilla allegedly consumed a suspected poisonous substance with her children, for the reasons known to her.
A close relative said they are not aware of the reasons which might have led Priscilla to act the way she did.
“I talked to her husband after we received the news, but he said they were both fine.
“He was surprised after the neighbours called him and notified him about the incident.”