Not really a belief, but the advert for galaxy chocolate, used to say "why have cotton when you can have silk?" so when i was young I used to refer to galaxy as "silk". In the middle of supermarkets i'd look to mum and say "could we get a bar of silk?"
and people would give us strange looks
A childhood belief about adverts

others believed things like this
- I used to dig a super deep hole thinking it
would transport me to the galaxy — Rafaella - I thought "The Hitchhiker's Guide to the Galaxy" was a somewhat casual manual for astronauts.— Katya
- i used to believe cotton candy was real cotton after going to chuckie cheese and my brother told me— jennifer
- When I was young, I used to believe that clouds were made of cotton— Anonim
- I used to think that cotton candy was made from actual cotton so I never wanted to try itAnon
- i used to belive that the cotton and the cotton candy were the same things and for this reason i ate both.— tiziana