What must a thief do, who was a child when he stole from several stores, some of which have closed and some of which are still open, and who now continuously gives to charity?

A boy is not held accountable before puberty, so there is no sin upon him. However, he is obliged to guarantee what he has damaged. If the aforementioned age is the age of puberty, then the questioner must offer sincere repentance, return the money to its owners or seek their forgiveness. There is no harm in using stratagems to return the money, such as making them believe it is a loan, or sending it via bank transfer. As for giving the money in charity, it is not sufficient except when there is no hope of returning the right to its owners. If they are found later, their right must be given to them.