What would happen if Allah had not made it obligatory to spend on one's wife and children, and what would their situation be like then?

Allah's rulings are based on mercy, wisdom, and justice, among which is the obligation of maintenance (nafaqa) for the wife and children, a ruling that serves the interests of people. The wife is confined to her husband, and withholding maintenance from her is an injustice. As for children, their maintenance is obligatory upon the father due to their lack of wealth or earnings, and abandoning their support is a form of neglect.