How can I have a taxonomy list that shows parent child relationship, but not allow the parent to be selected? Now and then I will come across a Drupal site that shows taxonomy terms to be selected in a drop down list. Example:

Fruit
    apple
    pear
Meat
    pork
    beef
..etc


And, while the child of each parent is selectable, the parent is not. How is this achieved, and how can I apply it to my taxonomy vocabulary who terms are 1 child deep?
Download and install this module http://drupal.org/project/term_reference_tree and
 check the Leaves only(Don't allow the user to select items that have children) option under manage fields-> click edit on taxonomy field.

It will select only the children not parent.