How To Hide The Child Category Until The Parent Category Is Clicked?

Hi,

I would like to know if there is a way that I could hide my child categories until the parent catergory is clicked?

For example, If I had a parent category titled “A” and in this category I had several child categories that started with the letter “A” I would like to be able to hide all the child categories until the user clicked on the actual parent category.

Is there any plugins that could do this or is there any simple way to achieve this?

Any help would be greatly appreciated.