I have a family member who has three children. Two of them are lovely, but her eldest son, who is now an adult, has proved to be a deeply disruptive individual. Even as a small child, he would deliberately and maliciously cause chaos in the household.
He intentionally injured visitors while pretending it was clumsiness or a mistake, and he deliberately damaged items of which he was jealous, such as his cousin's toys or his uncle's new car. You could guarantee that if he saw something desirable that belonged to someone else, he would find a way to 'accidentally' damage it.
He stole genuinely sentimental items because he enjoyed witnessing the grief caused by their loss. His desire to provoke his parents, even as a very young child, was almost pathological. Anything new or exciting in the household was always damaged or stolen. (I stayed there for a couple of days once RIP a pair of earrings I was incredibly fond of)
The eldest daughter never kept any of her personal possessions at home; she kept everything of value at a friend's house because she knew that when he was in a bad mood, he derived deep joy from the destruction of something that somebody else held value in.
It became progressively worse when he became a teenager and discovered alcohol and drugs, taking to them like a duck to water. He was regularly involved in fights, and his poor behaviour brought danger to the family home in the form of people throwing bricks through the windows after having disputes with him.
He violently assaulted his siblings and wider family members. He would break doors and smash windows if people didn't let him in immediately. He set fire to a neighbour's house ( allegedly) because that neighbour reported him to the police for a disturbance in the road and welfare concerns.
His mother and father were between a rock and a hard place because if they called the police on him and he was charged, then that would make him considerably less employable and more likely to never ever leave their house.
So they had him assessed for every condition they could. Especially as there was no triggering reason for this behaviour, but social services threw their hands up and said that he was at home and well cared for and that was the end of that.
He went away for a lads' holiday on some Greek island (From money likely gained by dealing drugs), and while he was gone, they moved house — They moved the family to a whole different country on very short notice, didn't contact anybody, didn't tell anybody where they went. Abandoned their house ( which, to be fair, was in negative equity) and decided to start again.
They still live abroad to this day.