What is the ruling on how pious children should treat their parents whom they see committing sins such as adultery and theft?

Whoever sees their parents or others committing a reprehensible act must change it with their hand, tongue, or heart, according to their ability, for the Prophet, peace and blessings be upon him, said: "Whoever among you sees a reprehensible act, let him change it with his hand; if he is unable, then with his tongue; and if he is unable, then with his heart—and that is the weakest of faith." So, if you are unable to prevent them from disobedience with your hand, then you must condemn it and show your disapproval, reminding them of Allah's punishment for the disobedient with gentle words and good counsel, while continuing to honor and obey them in matters that do not involve disobedience.