Is it an Islamic duty for a wife to take care of the newborn child of her husband's other wife? The only reason is that the other wife has to go to work in order to support her children from another marriage and therefore, she has no time to take care of her new born baby.
Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. A wife is not obliged to take care of her fellow wife's children regardless of their age. But since her fellow wife is working to spend on her children from her first husband, helping her do so is rewarded by Allah, provided that there is sincere intention to please Allah The Almighty. Allah knows best.
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