My oldest is about 5. Middle is nearly the same age as yours. As others said, we only spank for intentional disobedience. I hate doing it but it is the only thing that works. 9.9/10 times the threat of a spanking works wonders on the oldest.

We are just starting that with the youngest. So far, it hasn't been true spanking. Mostly just a pop on the hand when we tell him not to grab/touch something.