Federal Rule of Civil Procedure 17(c) provides: 'Whenever an infant or incompetent person has a representative, such as a general guardian, committee, conservator, or other like fiduciary, the representative may sue or defend on behalf of the infant or incompetent person. If an infant or incompetent person does not have a duly appointed representative he may sue by his next friend or by a guardian ad litem. The court shall appoint a guardian ad litem for an infant or incompetent person not otherwise represented in an action or shall make such other order as it deems proper for the protection of the infant or incompetent person.'
Under Federal Rule of Civil Procedure 17(b), the capacity of these plaintiffs to sue is determined by the law of state where the suit is taken. Under Pennsylvania law, a plaintiff who is a minor (defined as a person under the age of eighteen years) must be represented by a guardian who supervises and controls the action on his behalf. Pa. R. Civ. P. 2027; see Pa. R. Civ. P. 76 (definitions of 'minor' and 'majority').