Mont. Code Ann. § 40-6-110

The child must be made a party to the action. A minor must be represented by the minor's general guardian or a guardian ad litem appointed by the court. The child's mother or father may not represent the child as guardian or otherwise. The court may not appoint the department of public health and human services or any of its staff as guardian ad litem for the child. The natural mother, each person presumed to be the father under 40-6-105, and each person alleged to be the natural father must be made parties or, if not subject to the jurisdiction of the court, must be given notice of the action in a manner prescribed by the court and must be given an opportunity to be heard. The court may align the parties.