Is repentance for stealing money from siblings in childhood, without knowing the exact value, sufficient to clear one's conscience?

There is no sin upon a child for what he does, according to the hadith: "The pen has been lifted from three: from the sleeper until he awakens, from the child until he reaches puberty, and from the insane until he regains sanity."

A child is liable for what he damages of people's property, and he must return what he took without permission. Intentional and unintentional acts concerning people's property are the same; accountability is not a condition for guaranteeing it.

You must seek forgiveness from your siblings or fulfill their right regarding what you took from them, and estimate the value of the property in a way that clears your conscience.