Pontefract youngster Ben Kelly was on holiday in Skipsea, East Yorkshire, with his family when they were involved in the accident on Wednesday, July 29.
He had to be airlifted to hospital with life-threatening injuries and was left unconscious for two days.
But surgeons at Leeds General Infirmary (LGI) carried out a pioneering operation on a blood vessel in his heart and he is now recovering.
His great-uncle Andrew Sheward said: “It literally was a matter of Ben having the operation or he would have died.
“He had a tear on a blood vessel on his heart and they had to put a line in from his groin to the heart with a balloon to open it up.
“They had to get a surgeon from St Thomas’ Hospital in London to perform the operation and it was the first time that it had ever been done on a child.
“If it wasn’t for the surgeons at Leeds we would have lost him.”
Ben, from Nevison, was enjoying his first family holiday with his mum Kerrie-Ann and step-dad Andy Chester and his two-year-old sister Khloe Jean.
As well as the tearing his blood vessel, Ben also suffered a broken pelvis and a dislocated right thumb.
The rest of the family, who were two days into a week long stay at Skipsea Sands Holiday Park, suffered minor injuries and have been released from hospital. A man in the other vehicle which collided with the family was also injured.
Mr Sheward, 44, said: “Ben got the full brunt of the force because the car that hit them hit the door where he was sitting.
“Thankfully he is recovering now but this could have been a lot worse. He could have died had it not been for the surgeons.
“The rest of the family are doing okay. Andy is having to have some counselling because he was driving the car and he’s still a bit shaken.
“But their main priority ever since the crash has been Ben and they’re just so thankful that he is pulling through.”
An off-duty nurse helped the family and Ben until paramedics arrived at the accident scene at around 12.15pm on July 29.
Orchard Head Junior and Infant School pupil Ben was airlifted to LGI and had the operation on Thursday, July 30.
He remains in hospital but his condition is no longer described as life-threatening.
Mr Sheward said: “As a family we would like to thank everyone who helped from the surgeons to the off-duty nurse and paramedics who were there on the scene.
“If it wasn’t for them Ben would have died - it’s as simple as that.
“The family would also like to thank all of the staff at Orchard Head school who, even though it’s the holidays, have been so supportive. They’ve been fantastic.” Mr Sheward also called on people to pledge their support behind the Leeds Children’s Heart Surgery, which was earmarked for closure last year.
He said: “Five years ago we would have lost Ben because this kind of operation wouldn’t have been possible.
“The fact the unit could close is just unthinkable. If it did close and something like Ben’s accident was to happen to another child they probably wouldn’t survive.”
Mr Sheward said Ben is likely to be in hospital for a number of months while he continues his treatment and recovery.
He said: “It’s going to be a long process but he is over the first hurdle and we’re all just so thankful he has survived.”