Data point: a friend's 4yo who is being raised by agnostics but with a Christian grandmother opined this week "I bet Grandma believes in that," when some werewolves came on his cartoon, because his 4yo theory is that Grandma believes in supernatural stuff and he does not and Mom and Dad are somewhere in the middle. His parents are working with him on this because approaching other people with the idea that supernatural entities and events are an all or nothing proposition is not a very good idea.