Given your posts in the divorce thread, I’m assuming this isnt a theoretical, rather this is something you are concerned about vis-a-vis your own kids.
There are many signs of abuse however few signs prove 100% that it is abuse, as opposed to someone else. Take your kids to a trained mental health professional, and inform the professional that you are concerned about abuse possibly having taken place.
As for seeing it in adults, yes Joseph is right’ people who abuse were likely to have been abused as a child. But only about 25% of those who were abused turn into abusers. The other 75% all have different symptoms, some get the necessary help and use their abuse as a springboard to improve. Some deny it happened, some turn to addiction. Some turn to prostitution as a way of marginslizing the significants of the traumatic events
Good Luck