A childhood belief about rude bits

When I was little I thought that my big brother had a penis and I didn't, NOT because he was a boy and I was a girl, but because he was older. I thought I would later grow a penis (and that everyone did when they got old enough). For a long time I thought that whenever I pooped, THAT meant that I was trying to grow my penis, or at least that it was the growing penis inside oof me pushing the poopoo out!