The court observed that it would have had jurisdiction to hear an application for variation of the custody and access provisions of the original divorce order, as this would have constituted a true variation rather than a new cause of action. However, when the applicant abandoned those claims at the hearing and pursued only the sole guardianship claim, she removed the basis upon which the court had jurisdiction. The court also noted the distinction between guardianship rights under common law (which the father retained subject to section 3 of the Act) and sole guardianship under section 4, highlighting that sole guardianship carries additional powers including testamentary appointment of guardians and independent power to consent to the minor's marriage.