A 12-year-old Pretoria boy who was shot in the head on Saturday afternoon has died, Unitas hospital said.

Spokesperson Melisha Pather said he died while being treated.

The boy, his policewoman mother, and his three-month-old sibling were gunned down at their Centurion home at around midday.

Captain Annake van Niekerk and the baby were declared dead at the scene.

Van Niekerk was the captain at the Pretoria Criminal Records Division and lived alone with her two children.

The bodies were found by her ex-husband.

Police spokesperson Inspector Wanda Olivier said the woman's service pistol was found next to her body and it would be sent for forensic testing. Poliec were still busy trying to piece the evidence together.