A 25-year-old man is being questioned on suspicion of murder after the bodies of a mother and daughter were discovered in a house.
Neighbours said a four-year-old boy was taken from the property unharmed, but crying and wrapped in a blanket.
The bodies were found by an adult relative at an address on Ironside Road in Hemsworth, Sheffield, at around 7.40am on Tuesday, South Yorkshire Police said.
The two victims have not been officially named by police but are understood to be 42-year-old Tracy Donnelly and her 23-year-old daughter Louise Donnelly.
Police said a four-year-old boy, also a relative, was inside the property at the time of the incident. He has been named in reports as Tracy Donnelly's son Daniel.
A police spokesman said officers believed it was a domestic incident and the local community were not in any danger.
Alex Green, 23, said he understood there was screaming coming from the house early on Tuesday, adding that a couple had been heard arguing a couple of days previously. "I know a neighbour who said he heard both women screaming, then one woman stopped and then the other one stopped," Mr Green said.
Detectives are continuing to question the man who has been arrested on suspicion of murder and is detained in custody.
The scene remained cordoned off with blue police tape and one house appeared to be boarded up. Some residents were allowed through the cordon to lay flowers at the scene.
A post-mortem examination is due to take place today after which formal identification will take place, police said.