Is it permissible to use Zakat funds to treat a child's congenital deformity when his father is unable to afford the treatment due to his debts and limited income?

The treatment of a sick child is an obligation upon the father. If the father is unable to treat his son, whose maintenance is obligatory upon him, then he is considered poor and deserving of zakat. This is because a poor person is one who does not possess what suffices for his basic needs and for those he supports. Therefore, there is no religious impediment to giving him zakat for this purpose, as the need for treatment is urgent, and zakat addresses such needs.