Does a father's allocating a large portion of his saved salary to his youngest son from his new wife, without doing the same for his older children, constitute forbidden discrimination under Islamic law?

The fatwa we adhere to is the obligation of equal treatment among children in gifts and endowments, unless there is a need that necessitates preferring some of them. As for expenditures, equality is not obligatory due to the differing circumstances of the children. If your father singled out his child from another wife with a gift due to need or spent on him in a reasonable manner, there is no blame on him. However, if he preferred him in a gift merely because of the father's old age and the child's young age, then this is not permissible. What is obligatory upon the father is to treat his children equally, either by giving all the other children the same as he gave, or by taking back what he gave. The right of the parent is great and his injustice or mistreatment does not nullify his right over his child, and it is obligatory to honor him and treat him kindly in all circumstances.