I remember the time I popped my nephew's boy (3 years) quite hard on the keester. The kid was hellbent on getting near a very dangerous Bull (just cause he's so huge - 2000 lb) despite telling him to stay away several times.
Of course, the kid probably thought I was just being a meanie for popping him, and I really didn't care - I was just scared he would get hurt, and relieved that I had caught him before he got too close. So, yeah...I guess he saw it as nothing but a "Penalty" from a capricious uncle, and I saw it as something quite different. And his father saw it as a job well done.
Later on when the boy cooled down, we took great pains to explain why Big Bulls are so dangerous - just like Big Cars and Trucks. I don't know if the lesson stuck, but I hope it did.
What did the spanking achieve? If he was 3 you could easily restrain him from the bull by simply picking him up. In fact that would be easier than spanking. All the spanking did was confuse the kid as to why Uncle Jules was hitting him.
Hitting is wrong, Uncle Jules just hit me. Why isn't Uncle Jules being punished? What the **** just happened to our carefully constructed system of rules? Can I hit Uncle Jules back? Can I hit my sister when I'm older like Uncle Jules? Do I have to wear tacky clothes like Uncle Jules to hit people?
Picking the child up creates far less confusion, safely removes them form the danger, and makes the subsequent explanation easier. You don't have to wait as long for them to settle down and the immediacy of the explanation has some meaning.