JJ: “Could it be that the halachos were written at times when the goyim accepted hitting kids and that’s why it was considered acceptable?”
No. That certainly was not the reason the Halacha was set to what it is.
“Btw if that answer is no then I why would the halachah change now?”
The Halacha did not change.
ubiq: “Rabbeinu Gershom’s cherem was liekly done due to “western sensibilities” arguably “changing halacha””
1. There’s absolutely no basis to make that argument. If there was, you’d have been able to cite a legitimate or authorative source for such an assertion.
2. Even if you did make that incorrect argument, rabbonim making a gezeira prohibiting something halachicly permitted is:
a) not a new or changed Halacha but rather a gezeira or geder
b) can be done unlike permitting something that’s halachicly prohibited
c) in the example at hand, unlike Cherem R”G, the rabbonim as a factual matter have not collectively made a gezeira accepted by the Klal that prohibited corporal punishment of children
d) in fact, Halacha from Tanach through Chazal through explicitly paskened in Shulchan Aruch which no halachic authority argues against, not only permit corporal punishment but rule that it is mandatory when the circumstances warrant it.