A woman and two children have been found dead at a house at Hillier, near Gawler, on Adelaide's northern outskirts.

Police were called to the house in Jack Cooper Drive at 1:30pm.

Officers discovered the bodies of a six-year-old girl, five-year-old boy and 29-year-old woman inside the house.

Chief Inspector Alby Quinn said police were met by three men outside the home when they arrived.

"A 30-year-old male has been arrested and he will be charged with murder," he said.

"This matter doesn't involve any other people, and it does at this stage appear to be domestic-related."

The man was taken to the Lyell McEwin Hospital and later discharged, but remains in police custody for questioning.

A neighbour, who gave his name as Hughie, said he was shocked to arrive home from work to the news of the deaths.

"I'm actually shaking, it's devastating, shocking," he said.

"Everyone, just about, knows everyone around here.

"Sad, it's always the kids who get hurt isn't it?"

Police were expected to remain at the Hillier property for several hours to complete their forensic investigation of the scene.