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 this morning.
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.
Neighbours raised the alarm after being woken in the early hours. They reported seeing flames and smoke billowing from the house.
The force confirmed that a car was also found alight a short distance from the house.
The vehicle 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.
Firefighters called to the scene described the house as being "100% well alight", with flames coming from the front and back doors.
A spokeswoman for the service said the father was not at home when the blaze broke out.
The children who died at the scene are believed to have been two boys, aged six and 13, and an 11-year-old girl.
Sharon Pavey has lived in the house next door for 10 years. She said the family had only recently moved to the area and she believed the father worked at a hospital.