Four-year-old Jandre Botha died for refusing to call his mother's lesbian partner "daddy".
Now the two women will spend the next two decades in jail for his death.
Magistrate Retha Willemse on Monday referred to Hannelie Botha, the mother who allowed her lesbian partner, Engelina de Nysschen, to assault and kill her son, as a "passive participant" in his murder.
She sentenced De Nysschen to 20 years for murder, five years for assault and two years for defeating the ends of justice - an effective jail sentence of 25 years.
Botha, 31, got 15 years for her passive role in the murder. She was further sentenced to five years for assaulting the boy with the intention to do grievous bodily harm, and a further two years for misleading medical authorities and police officers about Jandre's cause of death.
The Vereeniging Magistrate's Court ruled that the five-year sentence must run concurrently with the two years before ordering that Botha stay behind bars for an effective 20 years.
The women were ordered never to own firearms upon their release.
When the two were convicted in March, the court found that Jandre died after he refused to call his mother's lover "daddy".
Lydia Nkomo and her daughter, Aletta Lesiba, who worked for the couple at their tuckshop, had told the court that De Nysschen had violently assaulted Jandre while demanding that he call her daddy.
On Monday, social worker Johanna Kruger asked the magistrate not to impose a prison sentence on Botha.
She said the court should consider the fact that Botha was sexually molested as a child by her mother's boyfriend. The assault had a negative impact on her.
The court also heard that Botha divorced Jan Botha because of his extramarital relationships and that he fathered a child with another woman while still married.
However, social worker Petra Tromp, who also assessed Botha, rejected the plea. Tromp argued that Botha should be given a prison sentence for failing to protect her child from De Nysschen.
She rejected defence lawyer Jakobus Hendrik Smit's view that Botha was a victim of abused woman syndrome.
Smit had argued that Botha was scared of her lesbian partner, who had often threatened to kill her if she ever left her.
"She had an option to contact her ex-husband and report the abuse to him,"said Tromp.
"She also had an option to contact her father and step-mother and ask them to come and fetch the child to live with them in Potgietersrus."
The magistrate, agreeing with Tromp, said Botha had failed to execute the child's legal right to be protected from De Nysschen.
She further said the court had battled to get the truth about what caused the assault, a situation compounded by Botha's refusal to testify under oath.
Willemse lambasted Botha for telling Jandre's father of his death only nine days after he was admitted to hospital.
Botha and De Nysschen are expected to apply for leave to appeal their sentences.