Three children who were found dead at a house in Surrey were all aged under four, police have said.
The youngsters were found alongside the body of a man in Bremer Road, Staines, on Saturday, and officers have confirmed that all four were related.
Police said post-mortem examinations and formal identification would take place in due course.
Neighbours said the family included twins and a floral tribute outside reads: “Rest in peace little ones. We will always think of you.”
Surrey Police said it was called by the ambulance service to Bremer Road, Spelthorne, at about 13:15 BST on Saturday.
The force said it was investigating and had referred itself to the Independent Office for Police Conduct (IOPC), due to previous contact with those involved.
It said at this stage, officers believe it to be an isolated incident with no third-party involvement.
The mother of the children and next-of-kin are aware of what has happened and are being supported by specialist officers, police said.
Det Ch Insp Gareth Hicks, who is leading the investigation, said: “This is a truly tragic incident and a thorough investigation is under way to establish exactly what happened.
“We would like to thank the local community for their support and understanding whilst we have been conducting our enquiries.
“We can also now update that whilst Bremer Road was closed for a significant amount of time yesterday, it has now fully reopened and there will continue to be a police presence in the area for the foreseeable.”
Lisa Townsend, Surrey’s Police and Crime Commissioner, said she was being kept regularly updated by senior officers as the investigation progressed.
She added: “My thoughts are with the family, friends and local community.”
A spokesman for the IOPC said on Saturday it had been notified by Surrey Police about the “tragic incident”.
They added: “We will be assessing a referral from the force to decide whether any action is required by the IOPC.”