What is the ruling of Islam on child molestation, and is it considered fornication, especially if the molester is a relative, and what should the children and wife do if they become aware of this, and should the wife leave him if he claims repentance then returns to doing it, or insists that he is not doing anything unlawful?

Child sexual abuse is a forbidden enormity, and it is even more heinous when committed by relatives. Children must advise their father, the abuser, with wisdom and gentleness, and conceal his act unless a greater benefit necessitates informing someone to change the evil. If a wife is certain of her husband's abuse, she must forbid and advise him. If he does not repent, it is better for her to leave him through divorce or khul'. It is not permissible to accuse anyone of a sin based merely on suspicion.