N.H. Rev. Stat. Ann. § 464-A:41

When before or during the hearing on any proceeding in any court it appears to the court that the interest or rights of a legally incapacitated person by age or other cause or circumstance are not fully represented or upon the request of any interested person, the court may appoint a competent and disinterested person to act as guardian ad litem for such legally incapacitated person and to represent such person's interest in the case. The guardian ad litem shall have none of the rights of the general guardian. The person appointed guardian ad litem shall make oath to perform such duty faithfully and impartially. A bond may be required of the guardian ad litem at the discretion of the court.