This is one problem I've never been able to figure out how to overcome. I have family in all positions on this, and honestly arguing with a devout believer is like talking to a brick wall. Eventually you just get to "because God says so", at which point you realize no matter how reasonable or informed your argument is it will never get through.
I'd flee to my parents' room because, like most six-year-olds, I believed that my parents possessed some magical ability to ward off homicidal, fire-breathing monsters that were easily eight times their size. I don't know exactly how I thought they would be able to protect me from the monster, but as far as I was concerned, my parents were forcefields of safety and that fire monster could go fuck itself.