I used to believe that you'd be certain heights at certain ages, and instead of growing gradually you'd just scale up at the exact moment that you were born on your birthday. I remember watching my sister closely for her 13th birthday (I was 7 or 8 at the time) and being really disappointed when she didn't suddenly grow a foot taller.
A childhood belief about getting older

others believed things like this
- I thought I was such a lucky and special kid, because I was born on the exact same day as my birthday.— ricolarno
- i thought that when it was your birthday you grow and then you didn't grow until a years time.— hello
- My sister uesd to think that you did a whole year's worth of growing in the night before your birthday.— Richard Davies
- I used to believe that on your birthday, you didn't advance to your next age until you ate your birthday cake.— Casi
- i used to think that if i didn't celebrate my birthday each year my younger sister would catch up with me— q
- Up until I was almost 11, I thought that a birthday suit was a special outfit you wore only on your birthdayAnon