What is the ruling of Islamic law regarding how to atone for the sin of consuming the property of orphans, given the impossibility of returning the money to some of them due to death, lack of need, or unknown whereabouts? Is it permissible to give it to other orphans?

Your sin is grave due to your betrayal of trust and your unlawful acquisition of others' money. However, your regret is repentance, and you must return the funds to their owners, as the Messenger of Allah, peace and blessings be upon him, said: "The hand is responsible for what it takes until it returns it."

To return the funds: If you were an agent for the donors, the orphans are either unspecified, in which case you can disburse the money to any orphans studying in kindergarten who meet the criteria for eligibility; or they are specified, in which case you must pay those who still meet the description for which the money was given. For those who no longer meet the description or have passed away, you must return the money to the donor.