I am sure no one sets out imagining they're going to slap their little children. Actually thinking about and planning what to do and how to approach disciplining a child before hand goes a long way to determining what you actually do in practice. The same way you might plan for any other eventuality or situation in life, assuming you do!
There are many ways to discipline a child without smacking them. The trouble is there is often an instinctive reaction to dish out a slap because maybe you're frustrated, embarrassed or even scared.
Perhaps the most important thing you can do is actually talking with as opposed to at your children so they learn and understand the value of verbal communications is more powerful than shrieking and having a tantrum.
Let them scream and carry on as long as you don't give in they'll soon learn it isn't the way to get what they want. Put them in their room until they've calmed down; as puma says take away their toys, sit them on the quiet step etc. Or, show them using their toys what will happen to them if they for example run into the road or go too near the fire, or whatever it that's worried you!
Part of the main problem for children is inconsistent boundaries, eventually giving in to their demands some of the time and not others. They are children. They don't know any better. They learn from you and want and are looking to you for guidance on how to behave. If they learn that if they carry on and on and on that you will eventually give in then that is what they will do.
In fact children learn about two thirds of everything they will learn if life in their formative years so they aren't stupid at all and in fact can be quite manipulative.
Anyone who has seen the BBC little angels or even teen angels will have seen the dramatic improvements in children and teenagers behaviour in just a few weeks of applying consistent boundaries.
The trouble with violence against children, you may call it a little smack if you want, is what happens when it becomes more than that or its a bit harder than you intended. When a smack becomes a slap or a clump to the head because your child dodges the blow and falls over and is seriously hurt.
Everyone assumes that they are rationale and reasoning and probably they are most of the time. But anger is a nasty adrenaline fueled emotion and things can quickly get out of control.
BTW I have never ever seen a child screaming in the street shut up because of a slap; rather the reverse making it worse for everyone.
Finally, you'll be pleased to know, that sometimes there is something serious behind a child's bad behaviour. My niece became a cheeky little madam when she first started school. It was put down to her starting school and mixing up with the other children. Also there was a new addition to the family so the timing wasn't great. Anyway, the health visitor recommended sending her to her room which did seem to work.
However it transpired that my niece was being bullied at school and my sister in law only found out because she came across some cartoon drawings in my niece had done and hidden in her room - when she was there calming down!
In the work that I did before coming to Turkey a lot of the children and young people I worked with had come to the attention of Social Services (I wasn't a Social Worker) because of bad behaviour in school. They were all being sexually abused by "uncles" family members or friends of the family or teachers.
There are plenty of resources via Google search for parents who want to adopt a non violent approach to bringing up their children.