What is the legal ruling on marrying a second wife when the first wife desires a divorce, and what is the impact of that on the children?

Allah has permitted a man to marry two, three, or four women. A wife is not entitled to seek divorce merely because her husband has married another, based on the Prophet's (peace be upon him) saying: "Any woman who asks her husband for divorce without a sound reason, the fragrance of Paradise will be forbidden to her." Therefore, the husband should keep his wife if he wishes, and she should fear Allah and retract her request for divorce, out of fear of the warning and to avoid negative consequences for the children and the family.