A fourth child has died following a house fire which police are treating as suspicious.
Police and firefighters were called to the house in Barn Mead, Harlow, Essex, at about 1am on Monday.
A woman and three of her children were taken to hospital, where they were pronounced dead.
A fourth child died later at the Princess Alexandra Hospital and a fifth remains in a critical condition. A man has been treated for minor injuries.
Senior investigating officer Detective Superintendent Rob Vinson said: "This is the still the early stages of our investigation into the tragic deaths of five members of one family - a mother and four of her young children.
"At this time we are investigating to see whether this fire was started deliberately and need anyone with information to contact us."
The force confirmed that a car was also found alight a short distance from this house. This was not connected to the family, who are believed to be of Asian origin; however, the car fire is also being treated as arson.
The house will be forensically examined to find out how the blaze started.
Mr Vinson added: "For the sake of the family, who are trying to come to terms with this tragic incident, I would ask for information from the public, especially in the Harlow area, to help us determine exactly what has happened."