In this one I'm actually the mean big sister, but about two years ago I managed to convince my little sister that Canada was down and Mexico was up. We were at the dinner table and my parents just played along. . .after dinner she went and found a map and then got mad at us but the look of utter confusion on her face and then the actual belief was absolutely worth it.
Perhaps the best part of the story. . .my sister was sixteen at the time :)
A childhood belief about places

others believed things like this
- My sister uesd to think that you did a whole year's worth of growing in the night before your birthday.— Richard Davies
- My sister thought (not more than one year ago, she is now 14) that John Doe was an actual person.— Brother to Natascha
- I used to belief sloths lived in trees outside my childhood home. My older sister told me so.Anon
- When my sister's father went to Seattle, my sister said "Is Attle nice?" She thought Attle was a person's name— zzo38
- Mom couldn't understand why at dinner time I wanted Chicken Pox.— Kristin
- I used to believe disneyland was under my sister bed. I was well dissapointed when I found out she was lying!— Joe B