Eight members of one family have been arrested in a child porn ring bust outside Pretoria, reports said on Friday.

According to The Times newspaper police raided four homes north of Pretoria in the early hours of Thursday.

Those arrested included a grandfather, 58, grandmother, 57, their two sons from previous relationships, aged 34 and 36, the grandfather's brother, 61, and his wife, 42, and their mentally disabled son, 28. The 26-year-old wife of one of the sons was also arrested.

They stand accused of sexually abusing four children, three boys and a girl, aged between four and 15.

Social workers became suspicious after two foster children -

who were removed from the families in March and October - started doing badly in school.

The eight will face charges of rape, indecent assault, sexual grooming of children and possession, manufacturing and distribution of child pornography.

They are expected to appear in court on Monday. - Sapa