Up until about kindergarten, I believed people used to live in black and white. Yeah, it's not exactly a question that pops up naturally and parents/adults can't be blamed for not thinking about this one.
I believed the furry folks and mechatronics at the fun fair to be real, deformed and angry live animals up until about age three or so. It was quite a relieve when I figured it out, as that stuff was super creepy. Like some evil monkey that popped out of some box that was far too small to hide a whole monkey in it.
Oh, and I still believe in God. I know he does not exist, I ain't stupid. But I know very well that the idea of God exists, and in my little bubble of multicultural, multi-faceted life experiences, God is of prime importance, especially when interacting with children from different cultures/religions/cults... and their parents. I just find God to be much more helpful and efficient than Santa Che, Saint Marx or Papa Smurf Engels.
If it weren't for the generally accepted notion of God, we'd be bashing each others heads in, and it wouldn't even be a proper survival of the fittest, it would be survival of the most ferocious.
That does not cover the aspect of religious fantards that kill and hate in the name of their respective, superiour God, mind you.