1) What science? I hate when people say "scientists say" without citing. that's like...school 101
2) young children do not "comprehend" everything. They don't always understand Logic. They understand stimulus. That's why babies put everything along with bugs in their mouths, because their most sensitive sense is taste. with that said: not all brains are wired the same. Some can see another child having an "ouchie" and say "oh no i'm not gonna do that", and some don't learn no matter what or how much they see until they try it out themselves.
Simple example: As a kid i remember seeing my mom going "oh, ah ouch ouch" when she lifted a hot plate to move it somehwere. that didn't register. I wanted to touch the hot plate, my mom told me not to touch because it causes and ouchie. I still didn't listen and (while she kept a close eye on me) she let me go ahead and reach for the hot plate and...guess what? ouchie! Never did it again. at young developmental age, children understand only "ouchie" and "yippie". that's just how we are wired because we dont understand logic
3) the first trick to being a good person is to learn self restraint. that's why, as kids, we get into lots of "oopsies"; because we have no concept of patience. we see, we want to act. controlled discipline (NOT BEATING) creates the first building blocks of developing self restraint. now SOMETIMES you can deliver the message non physically, but at times--because children don't have a clue about the meaning of term "consequence"--those blocks must be super imposed by the guardians.
final example: as a kid, I used to be fussy. I wasn't hit all the time, but there were some times I was being too bratty and cried because I wanted to take away the toy that belonged to another kid who didn't want to share. I got one good hit. Next time, at the toy store, I was about to get fussy again and cry because I wanted more than one toy. My parents gave me ONE look...BAM. I remember, i never got hit again.
Beatings are ABSOLUTELY wrong. that DOES cause psychological trauma. The benefit of controlled punishment is that it creates the necessary barriers to control the basic carnal desires every human being is born with. With that final thing said, my advise is do what my parents did. After being disciplined, and after the tears dried, they sat down and told me why i got hit and why i deserved it. Even if I didn't understand fully, at least I felt the sense of love that they did this to me not because they "hate me", but because of reasons I did not understand at the time to be wrong. The rule of thumb, NEVER HIT YOUR KIDS OUT OF ANGER