Four children have now died after their family's Land Rover crashed into a river in Lincolnshire on Sunday.
Nine were in the Land Rover when it crashed
Thor Gresham, five, and his sister Angel, four, were pronounced dead at Leicester Royal Infirmary on Tuesday.
Their sisters Willow, two, and Keavy, eight, died on Sunday and Monday. Another sister, Amber, nine is in a stable condition in hospital.
They were with their parents in a vehicle which careered into the River Witham near Tattershall Bridge.
An inquest is expected to open later this week into the death of Willow, who died at Lincoln County Hospital.
Her nine-year-old sister Amber remains in a stable condition in Leicester Royal Infirmary.
Nigel Gresham, 36, and his partner Sara Bolland, 31, were not seriously hurt, along with their 12-year-old son Liam and 13-year-old daughter Star.
Mr Gresham and Ms Bolland are the parents of all seven children involved in the accident and the family have always lived locally, police said.
Officers said some people had tried to rescue the car's occupants from the river.
Lincolnshire Police spokesman Sgt Andy Roach said it was believed the Land Rover lost control and plunged down an embankment into the River Witham.
The accident at 1550 BST on Sunday happened on a single track road as the car passed a white minibus towing a trailer containing canoes.
Sgt Dave Kay from Lincolnshire Police said family liaison officers were on hand to help the children's relatives.
"We're there at a distance," he said.
"We don't want to get too close to the family because of the devastation of losing one child and now we've lost four.
"As as a parent myself I just can't imagine what it must be like for those parents."