What is the ruling on money paid by a man to orphans: should it be kept until they grow up, or spent only on them, or mixed with the mother's money and spent on household expenses such as rent, electricity, food, and clothing for them and for her?

The money must be spent on the orphans immediately, as specified by the donor. It is not permissible to leave it in an account until they grow up. Their mother may keep it in the account and withdraw from it as needed. She may also mix it with household expenses if what she takes from it is reasonable and commensurate with their needs, as Allah Almighty says: "And they ask you concerning orphans. Say, 'Improvement for them is best. And if you mix with them, then they are your brothers. And Allah knows the corrupter from the reformer.'" (Al-Baqarah: 220).