All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The father-during his life time-may favor some of his children over others in maintenance or financial assistance, if there is a sound reason for that. For example, one of them needs a house, another needs to pay tuition fees, a third needs to spend on his family and the like. In this situation, they aren`t obliged to give back what their father had given to them since they are gifts and, on the contrary, it is desirable for the father to give gifts to his children during his life time.
However, if there was no sound reason for favoring some children over others when gifting, then it is disliked for the father to do so since the Messenger of Allah (PBUH) said: "Fear Allah and be just between your children (when gifting them)…" {Related by Bukhari & Muslim}. In addition, it is desirable for the child who was favored over others to divide that gift amongst his brothers and sisters equally so as to please them, maintain kinship ties and receive a great reward from Almighty Allah. However, if he refrained from doing that, then he isn`t considered sinful. And Allah Knows Best.