One who stole property before reaching the age of puberty cannot discharge his responsibility except by returning it
Question

I stole a few things (four or five things) from the grocery store and from one of my relatives when I was small, of primary school age, out of naughtiness and not because I was in any real need of those things. My question is: what must I do with regard to what I stole? Please note that I no longer have those things that I stole, so I cannot return them to them.
Praise be to Allah.Firstly:
In the answer to question no. 7833 we discussed the issue of stealing by children, and how to deal with the problem and what causes it.
Secondly:
If a child steals property or commits an offence against someone by destroying some of his property, injuring him or killing him, and the like, then the child is not sinning by doing so, because he is not yet accountable, but the right of the one against whom the offence was committed is not waived; rather the child is liable and must restore his property.
An-Nawawi (may Allah have mercy on him) said in al-Majmoo‘ (7/37):
Ibn al-Mundhir said: The scholars are unanimously agreed that offences committed by children must be compensated from their wealth. End quote.
These words were also quoted by Ibn Qudaamah in al-Mughni (3/108)
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) was asked about the ruling on someone who took some forbidden money from a number of people, before reaching the age of discernment. After he reached the age of discernment, he repented to his Lord and asked Him for forgiveness, and he wants to return the money to its owners, but he does not know how much that money was, but he has tried to work it out without wronging any of them, in sha Allah. There is also one of these people whose name he does not know or where he lives; can he give charity on his behalf or not?
He replied:
With regard to those whom he knows, he should give them their due according to what he has worked out, and according to what he thinks most likely to be correct, or he may seek their pardon and ask them to forgive him for what happened in the past. As for the one whose identity he does not know, and he does not know whether he is alive or dead, and does not know who his heirs are, then he may give it in charity on his behalf, with the intention that it be on behalf of the one to whom he owes that due. He should also repent to Allah sincerely. Then he will have discharged his duty in that regard, in sha Allah. End quote.
With regard to your not possessing the exact property that was stolen, because it has been used up, what you must do is return something similar or its value to its owner.
If returning these things to their owners will cause you embarrassment, then you do not have to tell them about it; rather the purpose is to restore their rights to them by any means.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) was asked about stolen property in a case where the one who took it has repented and wants to return it, but that would cause him some embarrassment.
He replied:
He has to return the property to its owners, if he knows who they are, and he has to return it to them in whatever way is possible, even if that is without them knowing that it is from him. He may send it to them via whoever he wants so that it will reach them, via mail or otherwise. It is not permissible for him not to return it; rather he must return it to them, if he knows who they are, by any means, in such a way that they will not know that it is from him. He could give it to someone to hand over to them and say to them: This was given to me by someone who says that it is rightfully yours, and he gave it to me to hand it over to you. Praise be to Allah. End quote.
See also the answer to question 31234
We ask Allah to bless you and to increase you in guidance and steadfastness.
And Allah knows best.