Answered by Shaykh Faraz Rabbani
Does that mean when the child gets older he has to pay whatever he stole back to the owner? And if yes, can he change his intention from the sadaqa he gave a year ago, intending to be free of what he stole? (if he doesn’t remember who he stole from?)
#5: The material consequences of the actions of children are of legal consideration, such as in theft, harming or destroying others’ property, even though they are not sinful. [Ibn Abidin]
Yes, the child or their guardian must return or (if not possible) pay back whatever they stole.
If the shop or owner can still be found, it would necessary to repay them directly.
If they cannot be found, then one clear one’s dues by giving the amount away in charity on their behalf, as discussed in the answer below.
And Allah alone gives success.