Count nodes in categories INCLUDING child categories?

How do I select the number of pages within a taxonomy term, including pages in it's child terms?

What I actually have to do is harder. I have to make a list of all the child terms of a given term, and the number of pages within each of those children. For example:

A list like: 

Mammals
   Big mammals (243 nodes)
   Small mammals (212 nodes)
   Tall mammals (91 nodes)

Where the taxonomy is like

Mammals
   Big mammals
      Bears
      Elepahants
   Small Mammals
      Mice
      Squirrels
      Chipmunks
   Tall mammals
      Girraffes

And then pages (nodes) are assigned to each category.  20 giraffe pages, 11 Bear pages, etc.

I'm very good with php what do you suggest?