What should one do who stole things as a child and does not know their owners now to return them to them?

It is recommended to improve one's deeds after repentance, rectify actions, and increase seeking forgiveness and performing good deeds such as prayer, fasting, and charity. If you do not know the owners of the minor items you took, then give their value in charity intending it on behalf of their owners so that Allah may forgive you and they do not become your adversaries on the Day of Resurrection.