When I was little I used to thing poincettias were called placentas. No one told me otherwise until I was about 12. I just remember being so happy to see so many placentas around Christmas time.
A childhood belief about plants

others believed things like this
- I was told that for every christmas carol i sang before christmas time santa would give me one less present!— K
- I thought the holiday was called "Merrychristmas" so I would tell people "happy merrychristmas"Anon
- "Christmas time
mistletoe and brine..."— Santa Puncher - I used to think an evil spirit type thing called Wango lived in my dog. I was terrified of that dog.— Franklin
- i used to think before clocks were invented, there was no such thing as time— nathan t
- That a dog humping someone's leg was just really happy. — Ruben