What is the ruling on a son taking money or things from his parents without their knowledge, and does the ruling change according to the the son's age?

It is not permissible for a son to take from his parents' money without their permission. If he does so without a legitimate Shar'i reason, he is liable for what he took, whether he is an adult or not. He must return its equivalent or its value. If he does not have money, it remains a debt upon him. The difference between an adult and a minor lies in the possibility of an adult being deemed sinful and having the حد السرقة (punishment for theft) applied to him if the conditions are met. Some scholars hold the view that the حد السرقة should be applied to an adult son if he steals from his father's money.