A girl and boy confirmed dead in Stafford on Sunday morning were aged two and three, murder investigation police have said.
The youngest, Meraj Ul Zahra, was discovered along with Abdul Momin Alfaateh at a home on Corporation Street at about 07:30 BST.
Both were injured and unresponsive, Staffordshire Police said.
A 43-year-old woman from the Stafford area, arrested on suspicion of murder, remained in custody, the force added.
The children’s next of kin have been informed and are being supported by specially trained officers.
In a statement, the force said the incident had been referred to the Independent Office for Police Conduct (IOPC).
An IOPC spokesperson said: “We were notified by Staffordshire Police of the death of two children in Stafford on Sunday 12 October where there was recent police contact prior to their death.
“We understand a referral is being made by the force, which once received, we will assess before deciding whether further action may be required by us.”
“We are working hard to understand more about what happened leading up to these two children tragically losing their lives,” said Det Insp Kirsty Oldfield.
She added: “We ask that people do not speculate at this stage as it is distressing for family and friends and could hinder our inquiries.”
Luke Browne, who lives on the street, said he had seen a forensic van and a police car parked there as he left for work on Sunday morning.
“It’s very sad,” he said, “children dying is a horror. It’s quite painful to hear [about] it.”
The 61-year-old book shop owner added: “I’ve only lived there a year but everybody I’ve met has been lovely.”
Sebastian Grzesiak, who also lives nearby, said he too was shocked.
“It’s a very quiet and friendly street,” he said.
A cordon remains in place at the scene.
“We understand that this incident may cause concern in the local community,” added Det Insp Oldfield.
“There is no threat to the wider public.”
Officers were called to the home by West Midlands Ambulance Service which attended at 07:26 BST.
“Sadly, it quickly became apparent nothing could be done to save [the children] and they were confirmed dead at the scene,” an ambulance service spokesperson said.
Anyone with information that could help with the investigation is asked to contact Staffordshire Police.