Are the returns on an orphan's money deposited in a government Islamic bank permissible or forbidden?

If the branch is independent of the usurious parent bank in its transactions and assets, and conducts its dealings according to Islamic Sharia, and invests its funds in permissible ways, then there is no harm in taking and benefiting from those profits. Otherwise, it is obligatory to dispose of them by spending them on the interests of Muslims and distributing them to the poor and needy.