I have many Parent Terms with child terms on a Vocabulary. I wanna use one of the parent terms on a content type as option. Is it possible to have a Term Reference field on a Parent Term instead of a Vocabulary?
Create a view that show the taxonomy terms that you want to have as options for selection (you will have to manipulate depth).
Then you create an Entity reference field on your content type that references a taxonomy term. When you add the field it will ask for Entity Selection mode. You select Views (the alternative is Simple), and then you select the view that you created above.