I suppose the parents are trying to get some sort of comfort in their mind and conscience, afterall, it's religion that most people turn to (even the atheists) when situations seem hopeless and completely out of their hands...
As for blaming God for this, remember none of this would have happened if the parents had only been a little more cautious about their children ... cause and consequence and all that. If anything, it has made parents around the world much more aware when it comes to taking care of their children, who knows how many other would-be missing children cases have been prevented as a result?
I really do hope Maddy is found nevertheless, she doesn't deserve to suffer for her parents mistake.