Jake Day, 28, and Cindy Braddock, 25, died after their 4WD left the road and rolled about 10km from their hometown of Kondinin, in WA's eastern wheatbelt.
Their young daughter and two sons were stranded with the vehicle with their dead parents for more than two days in hot conditions.
They were found dehydrated but alive by family friends and were flown to Perth Children's Hospital for treatment.
A GoFundMe seeks to collect $50,000 for funeral costs, medical expenses and support for the children.
More than $58,000 in donations had already been collected a day after the fundraiser was set up.
"Thank you everyone for the donations this is going to make a world of a difference in the kids' lives," organiser Casey Guyer wrote.
The children were doing well in hospital and were surrounded by family, she said.
On Wednesday, Mr Day's cousin Michael Read told reporters the couple's five-year-old daughter had saved her one-year-old brother's life.
"The five-year-old became unstuck in the vehicle and she then got the one-year-old out of the car seat when they were stuck in the car for the 55 hours in 30C heat," he said on Wednesday.
"If it wasn't for the five-year-old undoing the buckle on the one-year-old's seat he wouldn't be with us today."
Photos and television footage from the crash site show a baby bottle and clothing about 10m from a straight section of road, along with flowers and a handwritten note placed by a family member at the scene.
