For example, Zeus married his sister Hera, who were children of Cronos and Rhea (also married siblings) who, in turn, were children of a mother who married her own son. Subjectively speaking, almost every greek god has some sort of either incest and/or pedophile twist in their story.
Same in norse and egyptian mythologies. As far as I've read, even islam has some stories of that kind with Muhammad marrying a 6 year old child (correct me if I'm wrong on this one). And I'm sure you could find similar things somewhere in the bible or judaism.
In Ancient Greence was pederasty - young males having a sexual relationship with an adult (male). And while it technically doesn't count as pedophilia to have sex with 12-19 y/o's, I'd still put it in the same drawer morally. According to a quick Wikipedia overfly, that was also the case in multiple different countries of different eras as well. In addition, I've read that incest was openly practiced within nobility.
So how common and socially accepted was it among the normal folk and what has changed since then? From today's point of view, it's not understandable why especially pedophilia was accepted back then in the first place.
Generally speaking, the idea of Muhammad marrying a child is not based on evidence that's free of criticism. It's simply based on Sahih Bukhari which says that the Prophet married me when I was 6 and consummated the marriage when I was 9. This does come from Sahih Bukhari which is seen as widely accepted however there are multiple issues with the idea of her age. One problem is with Sahih Bukhari itself. Sahih Bukhari comes through Imam Bukhari however the Sahih Bukhari we have today comes through Farabri, a student of Imam Bukhari who was not seen as someone being reliable and no one vouched for him until around 200 years later.
The way marriage worked in Arabia was different to how it is now and generally, it doesn't make much sense for child marriages in that time, especially among the lower class. Muhammad after his first wife died had a few children who were between the ages of 1-6 and there are discussions between Muhammad and other people who were suggesting women for Muhammad to marry and the proposals were around 40 because Muhammad was looking for a woman to look after the house and to take care of the children. It doesn't make much sense for him to marry another child.
The general understanding from Arabia within that time was a girl must have hit puberty and she must understand what marriage is and she must consent. This is the understanding of scholars in Arabia from within a few centuries of Muhammad and there are authentic hadith mentioning that force marriage is forbidden and there must be explicit consent.
Paedophillia was not generally something that was practiced in Arabia. The vast majority of descriptions of the wives in Arabia describe them as women and they are generally seen as being women as opposed to children. The earliest ages of marriage would have been around 11 or at least when puberty began.
A common argument given by people who defend Sahih Bukhari is that people aged quicker then but the opposite is true. They aged and developed slower due to being malnourished.
Although Muslims do like to uphold the reliability of Bukhari as a source, it is problematic and the only reason why there are apologetics for this idea is because people want to accept Bukhari and to reject the age of Aisha is to accept the idea that Bukhari has problems with it. Based on various other hadith and discussions as well as customs at the time, child marriages were not really a thing.