Is a person considered sinful if they were subjected to the act of the people of Lot when they were young and unaware? And what is the solution for expiating that sin?

If the reprehensible act occurred before puberty, there is no sin, for the pen is lifted from the minor. However, if it occurred after puberty, then a great sin has been committed. Yet, the door to repentance is open. If one repents with sincere repentance and remorse, then repentance wipes away the sin, for "the one who repents from sin is like one who has no sin." And upon him is to increase in seeking forgiveness and performing good deeds, for "indeed, good deeds do away with ill deeds."