Is there anything a person who stole as a child and is now an adult, and who then returned what he could to those he stole from years later, should do?

There is no difference between an adult and a minor regarding the obligation to guarantee stolen goods and return them to their owners. However, the minor is absolved of sin. The thief must return the full amount of money to its owners, or donate it on their behalf if unable to reach them, guaranteeing it to them if possible in the future. If the owner of the money is unknown, it should be handed over to the ruler or donated on their behalf with the intention of guaranteeing it, and its reward will be for its owner. Repentance from injustices against people is not valid unless rights are returned to their owners. If unable to do so, one must resolve to fulfill them whenever possible.