RecruitingBiological interventionEvaluating the Pharmacokinetics, Pharmacodynamics, and Safety of Efgartigimod Administered Intravenously in Children With Generalized Myasthenia GravisThe purpose of this trial is to investigate the PK, PD, safety, and activity of efgartigimod IV in children and adolescents aged from 2 to less than 18 years of age with gMG. Trial details include: * The maximum trial duration for each individual participant will be approximately 28 weeks * The treatment duration will be 8 weeks for the dose-confirmatory part (Part A) and 18 weeks for the treatment response-confirmatory part (Part B)