The grandmother was at the Dzanani shopping complex with her daughter, the baby and other two grandchildren, aged three and five, on Sunday to collect social grants, Colonel Ronel Otto said.
The grandmother was approached by an unknown woman who offered to help her with the baby. The woman later gave the grandmother money and asked her to buy juice and an apple while she looked after the baby.
When the grandmother returned, the woman and baby were gone.
The woman was described as Venda speaking, tall, and slender. She was wearing a blue skirt and blue long-sleeved jacket.