Why have a belly button
When I was a very young child I asked my parents how did I get a belly button and what was it for.
I was told all babies were made of clay in heaven, when a couple wanted a baby a clay one was put on a conveyor belt and sent on its way to earth and to the couple. To make it into a living child Jesus stuck his finger in the clay version at the end of the conveyor belt and said "your done". Hence we all have a belly button.
Now later on in life what a useful thing to have, somewhere to put the salt when eating chips in bed for example
don't you just love those child stories you get told