The parent, who has not been named, was babysitting her friend’s daughter named Asanda Mbuku.
She killed Asanda with a rock after discovering her nine-year-old son had raped the toddler.
The mother dumped Asanda’s body in her back garden under sheets of corrugated iron next to a banana tree.
She then went to sleep with her daughter and rapist son with the body outside their bedroom window as the girl’s family searched for their child.
The mother, 32, sent her nine-year-old son to school the next day. He later told his aunt his sick secret and revealed where the body was.
A judge at Gauteng High Court in Pretoria, South Africa, sentenced the 32-year-old to 11 years in jail after she pleaded guilty to the murder and attempting to obstruct justice.
She cannot be identified in order to protect her son, who is now 11 and living in a safe house with his sister.
The court heard she had fed and put Asanda to bed after her parents asked her to babysit.
The woman was sentenced at Gauteng High Court in Pretoria
She later found the child half-naked and realised she had been raped by her son.The killer said: “I went to check and I found her lying on her back at the door. She was half-naked.
“I realised she was not moving and sprinkled her with water to wake her, but she did not.”
The killer told the court she feared Asanda would tell people she had been raped and her son would go to jail, if she woke up.
She said: “I took a rock and I hit her on her head to kill her. I hid her at the back of my garden. I did all this because my son had raped her and I did not want anyone to find out. I burnt her jacket and shoes.
“When her parents came to the house to fetch her, I said I did not know where she was. I am so sorry for what I did. I beg you for mercy.”
Judge Tshifhiwa Maumela said it was a pity the killer did not realise her son would not have been arrested for the rape.
In South Africa a child under 10 cannot be held criminally responsible for their actions.
The killer told the court she was sorry and wanted to take the opportunity to publicly apologise to Asanda’s mother, who was not in court.