simple tree in postgress

Hi, I'm a novice to postgress and need to constract a simple tree.
In my table I have:

regionID int
parentID int
name char

I need to do two functions:  find all the children of XXX parent and
find if an item is a child of an XXX parent.

I've looked in the discussions and I think there are at least two ways
of doing it:

(I'm pasting the following from one of the threads)

category_id | parent_id | sort_key |        name
-------------+-----------+----------+---------------------
           0 |           | aa       | Top
          10 |         0 | aaab     | Propaganda
          43 |        10 | aaabaa   | Quotes
          12 |        10 | aaabab   | Presentations
          70 |        10 | aaabai   | Waivers
           4 |        10 | aaabaj   | Legislation
          54 |         4 | aaabajaa | Youth in Politics
          36 |        10 | aaabak   | Statistics

This looks easy and I can see how to write queris using 'LIKE' on a
sort_key

The other way is to do preorder, inorder or postorder travrsals and
describe the level of the item and its traversal sequence number.  The
example I found was a bit confusing.  Can you point me to a place
where I can find more examples/explanations.

Are there other ways of doing it?  My tree would be small, maybe 5 - 7
levels and not too many leaves.  What are the advantages/disadvantages
of each method?
Is there a better way?  Does postgress offer any built in
functions/packages to work with simple trees?
I appreciate your advice.
Thank you
N.K.