I assumed things I came across in fairytales were make belief if I didn't know about it IRL. So when I saw a dwarf when I was 6 years old, I stared and shouted to my mom: "A dwarf! Look, it's a dwarf!"
I wasn't being insensitive, I was really excited, because I thought they only existed in Snow White, so I was as excited as if I'd seen a dragon or something like that.
When I was 4, I woke up in the middle of the night and went to my window and looked outside. I saw a lynx lying on a branch. Next morning I told my mom, who said it was probably a dream. I was so sure I really woke up and saw a lynx in that tree, I thought so until I was 13 and we went back there one day (we moved when I was still 5), and I realized that there was no way I could have seen a lynx that clearly because the trees were simply too far away to have seen it like I saw it.
When we moved back then, I somehow got the idea that when people move, they trade flats with whoever lived in their new place, so they get their old place. When my mom tried to explain that wasn't the case, I thought she didn't understand what I meant and was very frustrated. There was no way people didn't just trade houses, because otherwise someone would always be moving, and then the country would be so chaotic.
I believed the claim that if you meet badgers, they might attack and will bite your legs until they hear bones crunching. That's why you should always wear boots in the woods and fill them coal, so the badger will hear coal cracking.
Can't fault me for that belief though, I did after all learn it from our teacher in elementary school.