Heartbroken mum Louise James spoke to her young sons on the phone only moments before the family car slid off Buncrana pier in Co Donegal.
It has also emerged that the boys' devoted dad made a last desperate attempt to get the occupants out of the car by smashing a side window before drowning.
Ms James was at a hen party in Liverpool when the appalling tragedy happened.
Her partner Sean McGrotty (46), sons Evan (8) and Mark (12), mum Ruth Daniels (57) and 15-year-old sister Jodi-Lee Daniels all died when their car sank beneath the water.
Ms James' four-month-old daughter Rioghnach-Ann was rescued when she was passed through a window to hero rescuer Davitt Walsh.
When the Audi Q7 was recovered, the driver's window had been smashed and the boot was open.
Ms James was unaware of the horror that happened less than half-an-hour after she spoke to them until she returned home to Derry.
Pensioner Francis Crawford said the car, which was being driven by Mr McGrotty, got into some difficulty on the slipway, which was covered in algae, making it extremely slippery.
"I could hear screams from the car, the screams of children," he said. "There was nothing anyone could do.
"There was a young lad there, Davitt Walsh, and he stripped down to his underwear.
"I asked if he could swim, if he could go in, and he did.
"It was incredibly brave. He swam out to the car and came back with a baby girl.
"The car went under and the emergency services were here very fast, but there was nothing more they could do.
"Within the hour those poor people - that man I was talking to, those children who were screaming - were in body bags on the pier. I'll never forget the screams of those children."
Mr McGrotty, who worked as a glazier in Derry, lived with Ms James and their children at St Eithne's Park in the Ballymagroarty area of Derry.
Ms Daniels lived with her daughter Jodie-Lee and four sons - Joshua, who plays for Derry City, Kyle, Nathan and Jonathan - at Ederowen, also in Derry.
Northern Ireland's Deputy First Minister Martin McGuinness, who visited Ms James yesterday morning, said there is "utter devastation" in the family.
"That young woman that I met has to live with this for the rest of her life. How do you live with this?" he said.
Mark McGrotty was a first-year student at St Joseph's Secondary School and Evan, who had muscular dystrophy, went to St Eithne's Primary.
The principals of both schools visited the family home yesterday and were said to be very distressed.
Mr McGrotty's brother, Tommy, said of his nephews: "Mark would have been the quieter one, he would have been a bit more of a thinker.
"Evan was a joker, he loved getting involved and carrying on. He would play to get what he wanted.
"They were great kids, they wouldn't turn a bad word in your mouth. They just loved life."
Mr McGrotty said his brother and extended family had travelled to Buncrana for a "nice day out".
"Louise was away at a family function in England," he said. "Sean was out the night before and the granny had the kids. On the Sunday he decided to take them all out for dinner.
"He called down and took the wee ones out to Buncrana. They all had dinner and then he took them to the park along the shore.
"It must have been on the way home they decided to go look at the sunset on the pier and then, that's when it all went wrong, it ended in disaster.
County councillor Jack Murray witnessed the recovery operation.
Lifeboat workers slipped and fell on the pier as they tried to recover the victims' bodies.
"There was just silence as people watched," he said. "The town, the peninsula and communities in Derry and Donegal have been left completely stunned by this tragedy.
"Buncrana feels like it did after the Inishowen car crash tragedy when eight people died."
Among those who visited the scene yesterday were some of the relatives of the eight men who died in that crash only a few kilometres away in July 2010.
Tyre marks on the slipway, where Mr McGrotty had tried to manoeuvre out of trouble, were visible yesterday.
The slipway is used by the Lough Swilly ferry that connects with Rathmullan during the summer.
A sign at the top warns people not to trespass.
Donegal County Council did not respond to queries as to whether concerns had been raised about algae growth on the slip.
President Michael D Higgins yesterday extended his sympathies to the families.
"I have heard with the greatest sadness of the terrible loss of life of a family in Buncrana," he said. "My heart goes out to the family and loved ones."