What is the ruling on a father taking his son's money, adding some of his own money to it, then depositing it into the son's account, and repeating this action with the daughter but not with the male siblings?

A father must be just among his children in giving gifts, whether they are male or female. Favoring some over others without a legitimate Shar'i justification is considered injustice and oppression, for the Prophet, peace and blessings be upon him, said: "Fear Allah and be just among your children." Whoever singles out one of his children or differentiates between them without a legitimate Shar'i justification has sinned, and he must repent and return what he favored them with, or give the others what completes their share. If the father does not do so, then the one who was favored must return the excess to his siblings so that justice is achieved and the father's injustice is rectified, for it is not permissible for the favored one to take the excess, and he must divide all the wealth justly with his siblings.