My mother had a couple of good ones:
In Lucy in the Sky with Diamonds, she thought the line was "a girl with colitis goes by" (not "a girl with kaleidoscope eyes") and the refrain...
"Lucy in the Sky, Look Down" (Elton's version sounded more like this)
and
she thought the Hues Corporation disco song sounded like
"so I'd like to know where, you got the nose job..." (instead of ...."the notion")
A childhood belief about misheard lyrics

others believed things like this
- I thought that the line was "Lucy in the Sky with Linus" (not lucy in the sky with diamonds)— Forrest
- i used to believe that in the i love lucy days, everything really was in black and white— allison
- I used to believe that the heart at the beginning of the I Love Lucy Show was made of real chocolate.— Krissa
- I used to believe that a 'wolverine' was the girl version of a wolf. — Jelly
- When I was younger, I saw Madonna's video for "Material Girl". I thought she was singing "I'm a Cheerio Girl"!— Greg
- I always thought instead of saying "Im a material girl" Madonna was saying "Im a cheerio girl".— Tiffany