If my child doesn't understand the reason, is there any point in scolding?

At a stage where the reason isn't understood, long scolding rarely changes behavior and can just make the child shrink. In that case, showing and teaching the desirable behavior on the spot is more effective than scolding. For dangerous behavior, first stop it and make things safe, then change the environment so it's less likely to happen. Rather than ending at "no," convey the alternative behavior as a set—"do this"—with short words, demonstration, and pictures. Repeating it many times and recognizing the moment they manage it gradually builds "what to do."