Not quite a childhood belief, as this comes from my father who is in his 50s.... nonetheless, until about a year ago, he believed Tigers are green.
It came up in conversation about a year ago and we (the whole family) actually had to find a picture of one before he would believe all of us that they are actually orange....
A childhood belief about general

others believed things like this
- German tiger tanks shot out tigers, the invading army would get mauled to death by all the tigers— Bob
- i thought I got one year older when my family sang the birthday song.— I am the ghost
- Abba - Happy New Year
"Kangaroo year,
Kangaroo year..."— Santa Puncher - I believed that pigs could actually fly. I'm 13 and found out this year that they can't.— Boy I'm Blonde
- I believed that those who died would be resurrected a year later.— crow
- I used to belief sloths lived in trees outside my childhood home. My older sister told me so.Anon