There was an advert for some medicated capsule for sore throats or something which had the slogan "Suck 'em and see!". For years I thought the voiceover was saying 'Cychoman C', which I believed to be an important mineral or something like Vitamin C. Oh how my sister laughed at me.
A childhood belief about adverts

others believed things like this
- I thought a "cold sore" on your mouth was the same thing as "coleslaw" and so avoided eating it for years.— Helen (UK)
- I used to believed that "approximately" actually means "important".Anon
- I used to believe that a vitamin was a small animal
only recently I have found out that it is not true... :)— Sylwia - When there was an advert for a "3 peice suite" i thought it was a shop selling 3 P Sweet's!!!— Kate Parker
- I used to think it was the United STEAKS of America and that cows must be really important in the U.S.— Jake
- when I was little i was scared of vacuum cleaners. I thought they would suck me inside of them.— Julie