Just by coincidence, the five children in my family were born throughout the year, with the oldest being born earliest in the year on down to the youngest being born latest in the year. So it was my belief that the oldest kids always had their birthdays first, and the youngest last. I thought if someone was born on December 31st - their parents couldn't have any more children!
A childhood belief about birthdays

you weren't the only one
26 of you believed this
- I used to believe that I was older than my brother because I was born in June and he was born in OctoberAnon
- i used to think that i was older than my dad because my birthday was before his— zara
- My cousic used to think he was older than me because his birthday was in June and mine was in December.— //**...Ethan...**\\