With children as with dogs, if caught in the act, a smack is appropriate. Always explain why, never smack for no reason, never do the 'You wait till your Father gets home' trick as that lends fear and apprehension to what should be instant retribution.
Smacking should never be too hard and it should never be done because you are in a bad mood, it's not the child's fault you can't keep your temper under control.
Most importantly, both parents in a 2 parent household should keep the same rules, and any request from a child should always be answered by the question, 'Have you asked your Mother/Father' It is no good one parent saying different to the other, letting a child play one parent off against the other is a recipe for a badly behaved child.
Consistency is good for kids!
Giok