My brother and I have convinced all of our kids at one point or another that (if they continue to be bad) we will ship them off to join their evil twins in Pago Pago who were SOOOOO BAD that we sent them off at birth.
My wife and I have also convinced our 2 year old that the monster will get her if she doesn't lie down and get her diaper changed! (not sure how she will turn out as an adult now but what the heck)
A childhood belief about family

others believed things like this
- I had my wife convinced that Steven Hawking made his fortune as the original voice for the speak N spell toy.Anon
- I thought that "heck" was a less horrible version of hell for people who were only KIND OF evil.— Oizys
- a friend was convinced that his school was an asylum, and couldn't be convinced otherwiseAnon
- My mother convinced all of us kids in our family that the large rhubarb in the garden was a Man-Eating Plant. — H.Miller
- My brother once convinced me that the wind was "leftover hurricanes"— Tufty the Squirrel
- i used to believe i would 'catch up' to my big brother one day and we'd be twins.— lil' sis