A 37-year-old woman has been arrested on suspicion of murdering two children.
Police said the children, who the force described only as young, were discovered at a property in the Kent coastal town of Margate in the early hours of Thursday.
Less than an hour before they were found and taken to hospital, the woman was involved in a car crash and taken to hospital.
A Kent Police spokesman said: “At around 3.35am on Thursday 27 December 2018 officers attended a property in Castle Drive, Margate, due to concerns for the welfare of the occupants.
“The South East Coast Ambulance Service also attended and two young children were taken to hospital, where they were later declared deceased.
“Police remain at the scene and a 37-year-old woman from Margate has been arrested on suspicion of murder.
“The woman had been involved in a road traffic collision on the A299 Thanet Way at around 2.50am and was taken to hospital with minor injuries. She has now been discharged and taken into custody at a police station.”
Two uniformed police officers stood outside the terraced house in Castle Drive, which is on a new-build estate on the outskirts of Margate.
Forensics officers were earlier seen at the address.
It is believed they had not been living at the house very long, according to neighbours who said they did not know them.
Local priest Father John Taylor, who did not know those involved, said: “As a priest and as a parent, when I heard I was shocked, very disturbed and saddened.”
He added: “I came down to see if I could help and will say a prayer for the children.
“Something like this affects the whole community - just imagine how the neighbours feel and the rest of the family.”