Not the OP, but I think it’s not the slap on your bottom that should scare you as a kid, but the fear when thinking about the slap, and even more so, the thought that you made your parents so upset that they now have to slap you, even though they don’t want to.
Of course, that only works with parents who don’t resort to slapping their kids’ bottoms like it’s nothing (after a while you become accustomed to it as a kid, it doesn’t scare you anymore), and also parents who genuinely love their kids and who have a close and warm relationship with said kids, that way when the kid sees that he has upset his parents he knows he did something bad even before the slap (and in that way avoiding it altogether).
Trying to only use reason with kids who are 4 or 5 years old won’t work.
Of course, that only works with parents who don’t resort to slapping their kids’ bottoms like it’s nothing (after a while you become accustomed to it as a kid, it doesn’t scare you anymore), and also parents who genuinely love their kids and who have a close and warm relationship with said kids, that way when the kid sees that he has upset his parents he knows he did something bad even before the slap (and in that way avoiding it altogether).
Trying to only use reason with kids who are 4 or 5 years old won’t work.