Sorry to have gotten into this so late...I assume people are still reading this thread...
Anyways, as a parent my simple rule is this - there is never any place or any justification for a big person hitting a little person! Sorry...but to me a resort to physical punishment of our kids is a reflection of our own laziness or (as in the case of my father) our needs to be powerful.
I'd never punish my sub/slave in the midst of my anger...sure as hell would not do it with my kid.
What the BDSM arena teaches us is the central place of consent. Kids do not and cannot consent to being smacked or belted or slapped on the wrist - they don't have the capacity for it. But I would be wrong to believe I was able to make that kind of choice for my daughter...especially when being spanked in that kind of setting is all about the wrong kind of power...its painful, humiliating and disempowering...
Now that's off my chest...where's that slave of mine gotten to?