Here is my guess.
Most adults have figured out how to make sense of the world by matching what is in their brains with what exists in the real world. And most people do a pretty good job of responding to the cues of the real world: staying out of the path of fast moving vehicles, wearing warm clothes when it is cold, not falling off cliffs, keeping away from open flames, walking around the pile of dog poop on the sidewalk, ducking the swinging fist, etc.
But then there is religion. Religion tells people that what they think they see in the real world and are aware of through their brains does not in fact exist--it is an illusion, or a practice run for the real thing. The true world, the important world, is full of powerful invisible beings and can only be detected through supernatural means.
This is, of course, crazy. No angels push you out of the path of speeding trucks. There is no god, no Satan, no invisible fist swinging at you that you must somehow detect and duck. But a majority of the adult population of the world is trying to believe in some version of this.
Understandably, most people struggle with doubts about their religion, since it is clearly obvious that the claims of the religion are not factually true
. They have to reconcile these contradictions all the time, and fight the cognitive dissonance that results. When they teach the same religion to their kids, they hope that the kids will grow up full of solid faith and not have to deal with the same painful cognitive struggles.
And, at first most parents think, with relief, they have succeeded. Many kids are very theologically compliant and agreeable-- religious notions make perfect sense to kids. Of course they love Jesus or Krishna and believe in him. Because little kids don't have critical thinking skills and live in a world of fantasy anyway. We know this-- comic books, Halloween, ghost stories, Harry Potter, Santa Claus and the entire Disney empire are all based on this fact!
The problem comes when, at age 6 or 8 or 10 or 12, the kid realizes there actually is a big difference between fantasy and reality. Then the invisible friends die, there is no more boogie man in the closet, the magical dragons fly away, Santa is an old guy at the mall, the comics become fun books to read for escape, Greek myths are just that, the cartoons are a diversion for Saturday morning. And Jesus disappears as well.
At about that same age, lots of kids also become interested in the real magic of science: dinosaurs, weather, planets and outer space, magnets, animals, rocks, bugs, plants, toy trains and airplanes ie how the world really
works. Take an 8-year-old to the zoo, to a museum or just on a walk and try to keep up with the questions and observations--they are all scientists!
But religion is the special case, so the kids have to learn how important it is to lie and pretend that they have kept on believing that one set of fantasy ideas. Most will become struggling doubters, just like their parents. A few will break loose and shake off the "god delusion" usually after leaving their parent's home. Although as clearly made up, as fantastic and unreal as all the other myths and fairy tales, religion is supposed to remain true, because, why? Religion is just a scary bunch of stories and impossible rules.
At least the other fantasy stories are fun.