Exclude Taxonomy Term from Being Selected

I created a content type and used the Content Taxonomy field so users must select a term before publishing that content. My question is, if a parent term has children, how do I prevent users from selecting the parent terms in a vocabulary.

For example, here is the structure of the terms.

Vocabulary 1
-Parent Term 1
--Child Term 1
--Child Term 2
--Child Term 3
--Child Term 4
-Parent Term 2
--Child Term 1
--Child Term 2
--Child Term 3
--Child Term 4
--Child Term 5
--Child Term 6
-Parent Term 3
-Parent Term 4

In the drop down list, I want to prevent users from selecting Parent Term 1 and Parent Term 2. Is this possible?