Will my repentance be accepted and will God forgive me if I stole money when I was young, knowing that I do not remember whether or not I had reached puberty, and must I return the money for my repentance and forgiveness to be complete?

What was taken from the father's money unjustly must be returned, whether it was before or after reaching puberty. It is obligatory to return the amount that absolves one's responsibility, unless the rightful owner forgives it. If one is unable to return it and passes away, it is hoped that Allah will forgive him.