A family member of the three young children who survived a car crash that killed their parents in Western Australia has hinted at how the young couple died.

Cindy Braddock, 25, and Jake Day, 28, were killed near their home at Kondinin in the Wheatbelt region in the early hours of Christmas Day.

Their five-year-old daughter and two sons, aged two and one, survived in the flipped wreckage for two days in scorching heat before being found by a relative.

Day’s cousin Michael Read gave insight into how the crash took place by warning others against driving late at night.

“Know what your body limit is, don’t drive tired,” he told ABC News.

Jake Day and Cindy Braddock died in Western Australia on Christmas Day. Their three young children survived for two days before being found by family members. Photo / 7 News

“If you’re going to want to be somewhere, stay the night at a family’s place. It’s not worth it.”

Petrol station worker Nathan O’Donnell said he saw the family just before they embarked on the hours-long roadtrip just after 1am on Christmas morning.

 “They then got out, put fuel in, then they came in, they went to the toilet, they came and bought drinks and snacks and stuff for the road,” he said.

“He looked exhausted … he didn’t buy a coffee. Then he left, I told him good luck with the long drive.

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“Unfortunately, he never made it.”

All three children were at Perth Children’s Hospital in a stable condition on Wednesday.

Speaking outside the hospital, Day’s cousin, Michael Read, told of the children’s harrowing ordeal.

“What I’ve gathered is the 5-year-old became unstuck in the vehicle, and she then got the 1-year-old out of the car seat, then they were stuck in the car for 55 hours in 30-degree heat,” he told the ABC.

“It would have been hard for the three children to be in the car for that whole time. Nobody knows what they went through.

“And if it wasn’t for the 5-year-old undoing the buckle of the 1-year old’s car seat, he wouldn’t be with us today.”

“But all the kids are doing fine. They should be out within the next couple of days.”

Jake Day, left, and Cindy Braddock, right, were killed when their car rolled 10km from home in Western Australia on Christmas Day. Photo / Facebook

He said the family were “going bit by bit” on what was next for the children.

“It is hard, having three kids now growing up with nobody. Apart from other family members,” he told the ABC.

“We’re going bit by bit at the moment.”

Braddock, Day and their children, all under the age of 5, were reported missing on Christmas Day when they didn’t show up to a family celebration.

They’d last been seen leaving Northam, a town in Western Australia’s Wheatbelt about 100km east of Perth, at 1am on Christmas Day.

The family was making the 200km journey back home to Kondinin before to spend what was left of Christmas with Day’s mother.

“My understanding was they left Northam early so Jack could be with his mum on Christmas,” his cousin Michael Read told 7NEWS.

However, on Tuesday evening, police said the family’s maroon Land Rover had been found by another family member, 10km from the town.

“[I’m] pretty broken, not only have I lost my cousin, but one of my close friends... basically, we’re just taking one day at a time,” Mr Read said.

Jake Day and Cindy Braddock were found dead in their car after it rolled on Christmas Day while they were driving in Western Australia. Their three young children survived. Photos / WA Police

Braddock and Day were both found dead inside the vehicle.

Two of the children, a 5-year-old girl and 2-year-old boy, were outside the vehicle, while a 2-month-old baby was still inside.

The youngest child suffered a significant head injury and is in a serious condition.

The other two children are understood to be in stable condition.

Read said the community would be devastated by the loss of the young parents.

“They were really good parents, always good to have a joke and a beer with,” he said.

“They are going to be pretty missed by everybody — not just family and friends but the community as well.

He described his cousin as a “bubbly person” who was just “someone you could always get along with”.

He said Braddock was “overprotective of her children” who “always want mum”.

-By Liam Beatty and Madeleine Achenza
news.com.au