All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
A child is not liable for the Hadd (i.e. the corporal punishment determined by the Islamic Law) of theft or any other Hadd, and he does not bear a sin for it, because he is not competent for religious assignments, which is one of the conditions for the implementation of the penalty. Ibn Qudaamah said in Al-Mughni: “As for the conditions of sanity and reaching puberty, there is no difference of opinion among the scholars that they are stipulated for the implementation of the Hadd and for the validity of a confession because a child and an insane person are not held accountable for their deeds, and there is no consideration for the statements they make. It was narrated on the authority of ‘Ali that the Prophet said: ‘The pen is lifted (stopped from writing the deeds) from three kinds of people: a sleeping person until he wakes up, a child till he reaches puberty, and an insane person till he regains his sanity.’ [Abu Daawood and At-Tirmithi] [End of quote]
Al-Mawsoo‘ah Al-Fiqhiyyah reads: “There is no difference of opinion among the jurists that the Hadd is only applied on a person who is competent for religious assignments, namely a sane person who has reached puberty.” [End of quote]
However, waiving the Hadd and the sinfulness does not necessitate that the guarantee is waived as well. Rather, a minor is required to guarantee what he stole, and it is incumbent on him to return it to its rightful owner. If he knows the owner and can deliver the stolen item to him, he must do so. But if he does not know the rightful owner or cannot deliver the stolen item to him and seek his forgiveness, he donates the value of the stolen item in charity on behalf of the rightful owner. If he does not know the value of the stolen item, he should prudently give in charity an amount that he believes would most likely clear his liability from the obligation, and Allah, The Exalted, does not charge a soul beyond its capacity.
Allah Knows best.