N.H. Rev. Stat. Ann. § 170-C:8

When termination of the parent-child relationship is sought under RSA 170-C:5, IV, the court shall appoint a guardian ad litem for the alleged incompetent parent. The court shall appoint a guardian ad litem to represent the interests of the child in all termination hearings. The court may, in any other case, appoint a guardian ad litem, as may be deemed necessary or desirable, for any party.