I was of the impression that groups such as this do not believe in medicine at all, so even an older person would not go to the doctor. They don't want to interfere with god's work or plan. That wouldn't apply to a car but would apply to the body. I don't know if these parents are of that sort of thinking though. I am sure there is a lot of variation.
Jesus may be the Great Physician, but he's a rubbish mechanic.
All the new cars are so computerized these days.