Five-year-old Gracie Mackay, from Muir of Ord, Ross-shire, passed away at Glasgow's Royal Hospital for Sick Children after the Canadian-style canoe they were travelling in on a day out overturned in Loch Gairloch.
Early yesterday morning, police confirmed that two-year-old Jamie Beaton and his five-year-old brother Ewen, from Beauly, Inverness-shire, had died after being rescued.
Meanwhile, hopes of finding the brothers' 32-year-old father Ewen Beaton alive faded after more than a day of searching.
Locals said the three children died despite wearing lifejackets. It was unclear whether the fathers were using buoyancy aids.
Gracie, who had been plucked from the seawater loch, was one of six people from two families in a canoe which capsized off Gairloch on Sunday afternoon.
Her delivery driver father Garry and eight-year-old sister Callie swam more than 500 metres to shore to raise the alarm.
Gracie was initially flown to Broadford Hospital on Skye and was later transferred by Royal Navy helicopter to Glasgow, where her parents had remained at her bedside.
As police identified those who died, the Beaton family told of their heartbreak.
In a statement, they said: "We are utterly devastated by what has happened and the loss of our beautiful little boys. We appreciate all that has and is being done by emergency services to find their adoring father, Ewen."
Meanwhile, coastguards questioned the suitability of the canoe they had been using.
Peter Godding, of Stornoway Coastguard, who co-ordinated the search, said the Canadian-style canoe had "no inherent buoyancy - and is quite an unstable canoe unless you are with people who are experienced".
He added: "If you get a few people in them they can be quite dangerous, particularly if somebody stands up or leans over."
Local boats were involved in the rescue operation and Gracie was found by James Cameron, whose family runs the Sands Caravan and Camping site in Gairloch.
He was returning from a fishing trip when he heard the boat had capsized in a stretch of water known as Caolas Beag and joined the search. They found the girl after 15 minutes.
He said: "She was face down and unconscious. She had her buoyancy aid on. It was keeping her afloat but wasn't keeping her head out of the water."
Eight-year-old Callie, who swam to shore,
has been described by police as courageous.
Ann Aaron, who was among those who helped the child, said the father collapsed in a heap as he told onlookers there were children in the water.
Referring to Callie, she said: "I just think she was very brave. She was just a normal wee girl who was cold and wet and we did our best to look after her until we got her back to the [nearby caravan site].
"She was asking about the other children. She knew her daddy was OK."
A family friend of the Mackays said: "Garry was very upset. One minute they were in the canoe, the next minute it had capsized. Within seconds, the kids had floated away from him and he couldn't reach them.
"We just can't believe how a pleasant Sunday afternoon can go so badly wrong. It was only a couple of days ago that the kids were playing in my garden."
Ewen, five, was a primary one pupil at Teanassie Primary School, near Beauly. His brother was due to start nursery there this year.
James Martin, chairman of the school's parent council, said: "The school community is devastated. The Beatons are a well-known and highly respected family and the impact of their loss will be felt throughout the community."
After police, Stornoway Coastguard, lifeboats from Lochinver and Portree and the Red Cross were involved in the search operation, coastguard officials said there was little hope of Mr Beaton being found alive and their mission was being treated as a recovery operation.
However, Mr Godding said: "Miracles do happen sometimes."