I agree speakout. Parents who hit their children know it's wrong because they always try to minimise it by calling it a "tap" or some other stupid word.
I used the word 'tap' as that's the word that best defines what I have occasionally done. To use 'smack' may have implied 'beating' which it wasn't remotely close to!
To regard a tap as assault is a bit like believing that a crowd applauding is engaging in mass self-harm!
Despite this, I am in favour of a ban on smacking. I would help emphasise that using physical pain as a means of punishing children isn't appropriate. However, a smack would need to be defined, and would need to differ from the definition of assault between adults, as an adult should not engage in physical contact if the other adult does not consent. However, a parent clearly needs to be able to make physical contact with their young child irrespective of their consent. I would legally define a smack as any contact that causes more than momentary minor pain. That would remove a harmless tap on the shoulder from being considered a smack for instance.