I used to think that when you had to give your 'daytime telephone number', it meant that your number would change when people called you at night!
I thought that 'burning' DVDs and CDs was literally incinerating them.
When I was seven, my dad went on about how liquid made computers short out, so when a character in a YouTube video I was watching started to cry, I was worried that'd make the computer short out!
I used to think that the world doesn’t spin because we aren’t thrown against the walls while trying to move or just being idle.
When I learned from Jon Lee in S Club 7 that tanning beds are meant to be unhealthy because they can burn your skin and give you cancer, or even kill you if you get stuck inside and burnt to death, I thought they were just another term for deckchairs, before I knew what they actually were. Would make more sense to call them machines instead of beds. I kept thinking 'why is it bad to lie on a deckchair with a towel, everyone does that in Summer!'
Not sure if I really believed this, but I might have thought that the BT voicemail lady (Eleanor Bron) was really talking to you on the phone, instead of her voice being recorded. Creepy eh?:?
There is the common children's belief that stars really are tiny things shining in space, although they are suns, just like ours in the universe.
This is actually an early adolescence belief: when I was about twelve through fourteen, I thought viral videos were ones that gave your computer viruses.
I thought opium was an element.
One time, I was playing in the living room while my mother was watching something and a character on the TV said, "Oh! I forgot to close the fridge door!", and so Mum turned to me and said something along the lines of, "Don't you ever forget to close the fridge door."
Then later, I saw an episode of "Spongebob Squarepants" (which is this wacky cartoon about a talking sea sponge) where Spongebob gets sick from leaving his fridge open.
Both of those made me think that every time you left the fridge door open, something random, but always very bad, would happen.