I have a number of top-level categories including "News" and "Sport". They each have multiple levels of child categories as shown below.

• News

  • Australia
    • NSW
      • Sydney

• Sports

• Cycling

  • Road Cycling
  • BMX

• Triathlon

In my loop I want to display a single category - what ever is the deepest child category of "Sport".

I have found some code on StackOverflow that does returns the deepest child category, but not from a specific category. It returns the the deepest child category from all top-level categories. So if a post is in two categories (Sydney and Triathlon) the code shows Sydney as the deepest child category. I somehow need to specify that which top-level category I want the deepest child to come from. In this case that would be "Sport" and the deepest child cat would therefore be "Triathlon".