But when they are children, you discipline them
Discipline, yes.
Spanking is not discipline. It teaches nothing that can't be gotten at, by another means.
Why do you justify hitting someone your charged with caring for? That says a lot about your supposed morals.
I used to believe exactly like you did. Except I learned, and changed my behavior. Part of that was from raising animals. Where striking them, does not do anything but create issues. We as people and as children especially are no different.
Edit: I know that you will take this to your grav as being alright, and that it's completely justifiable, so I'm stepping away (and not responding to you).
May your God have the mercy on you, you can't and didn't show your children.