A childhood belief about giving birth

I used to believe that before my siblings and I were born, we all lived one on top of another in my mom's belly, and instead of coming out as babies, we came out as old as we were at the time that I thought this. So, my sister would’ve come out a 15-year old, my brothers 14 and 5, and me 4. I wondered, too, how we all fit in there, because we were much bigger than my mom’s tummy!