[drupal-support] View child categories on category's main page?

[Steven Wittens]

There are several taxonomy modules in contrib which can display 
navigation blocks with categories. Check the module list on drupal.org 
for modules who have "taxonomy" is their name.

As far as you other question, this is easy: the taxonomy URLs support a 
depth parameter, which specifies how many levels of child categories to 
include. You can specify a number, or "all" to include all children.

e.g. change: taxonomy/term/1234 -> taxonomy/term/1234/all

However, Drupal will not use these URLs by default. You can use them in 
custom links and path aliases though.

Steven Wittens