A childhood belief about i'm different

I used to believe that my family were all millionaires but my two brothers, my sister and myself were being brought up in an ordinary household so we could be taught the real value of money and did not grow up spoilt. I remember thinking that my mother would tell us all when we turned eighteen. I must have believed this until I was at least twelve because I was sure that my brother and sister, who are both over six years older than me, already knew and were keeping the family secret from me.