A "down to earth" couple killed in a car crash just one day after their seventh wedding anniversary have left behind four children.

Sabine Mather, 31, and James Mather, 36, died in WA's South West region after colliding head-on with another car that was towing a caravan.

The couple had been on a "weekend away celebrating their anniversary" and the children were not in the car with them.

Tributes have been left for the couple.

“My best friend. My best man. THE best man. I love you Jim Mather. You two were so perfect together. I love you too Sabine Mather,” friend Timothy Hughes wrote on Facebook.

“My best friend for 36 years. You will never be forgotten.”

Jake Baarsoe, who worked with Mr Mather, said he was "absolutely heartbroken".

“Jim was such an important part of our team. Such a loving and caring guy that everyone looked up to,” he posted.

“Have never met anyone as optimistic and outgoing as he was. He will be truly missed. “

Fabienne Mckirdy, Mrs Mather's cousin has set up a GoFundMe page to cover funeral costs and the future care of the four children.

“Those who knew Sabine and Jim Mather would describe them as a friendly, caring, and down to earth couple who were loved by everyone they met,” she wrote.

“They were parents who would do anything for their children.

“Sadly Jethro, 7, and Isaac, 5, are now orphaned, and Jim’s older daughters Ella-Jade, 13, and Sofia, 15, have lost their father.

“Jethro and Isaac will now be raised by their grandparents, Elke and Steve.

“Jim’s older girls, Ella-Jade and Sofia, will living with their mum, Alicia.”

The emotional devastation has been made worse by the unexpected financial implications of raising the children without the income of their parents.

“Elke and Steve will now need to put aside their retirement plans to instead focus on raising the two young boys,” she said.

“Ella-Jade and Sofia will be living with their mum, and now need to come to terms with the devastating fact they will not see their father again. It is absolutely devastating for everyone.

“The family needs all the help they can get during this sad time.

“We can’t bring back Jim and Sabine, but we can help to ease the financial burdens that lie ahead.”