The home of missing mum Samantha Kelly and a neighbouring house are being searched as detectives question three people over her disappearance three weeks ago.
Ms Kelly, 39, was last seen at a shopping strip near her home in the Bendigo suburb of Kangaroo Flat on January 20, and police hold fears for her safety.
Homicide detectives and local police are searching a home in Kangaroo Flat and the rear bungalow where Ms Kelly lives.
The three people were arrested late on Thursday afternoon and have been taken to Bendigo police station for questioning, a Victoria Police spokesman said.
Ms Kelly was reported missing more than two weeks after she was last sighted by her NSW-based brother, Michael Kelly.
The children, the youngest of whom is one, are now being cared for by Mr Kelly and his partner Danielle Stevenson.
Ms Stevenson posted a picture of the children to her Facebook page.
Three of them have had their heads shaved, but Ms Stevenson says she does not know why.
Detective Senior Sergeant Shane O'Connell earlier told reporters police hold grave concerns for Ms Kelly's safety.
"It's out of character for Sam to go missing under these circumstances," he said.
"The youngest one has turned one recently and she missed that first birthday, which is very unusual."
Ms Kelly has not accessed bank accounts or used her phone.
It's believed at least 10 people have so far been questioned over her disappearance.