A Nickel's Worth

In the 1940's, when I was about five or six years old, my sister Mousie, being a nice person and loving her baby brother, wanted to trade me a dime for a nickel. She kept trying to convince me that the dime was worth more, but I still wouldn't trade with her. After all, in my young mind, I thought that if the nickel was bigger, it must be worth more. Even now, in my middle 70's, it still mystifies me why anyone would make the bigger coin worth less.