The purpose of this study is to determine the effect of nipocalimab on total serum immunoglobulin G (IgG) in pediatric participants 2 to less than (\<) 18 years of age (globally) and 8 to \<18 years of age (for Unites Stated (US) sites only), the safety and tolerability of treatment with nipocalimab in children and adolescents and to evaluate the pharmacokinetics (PK) of nipocalimab in children and adolescents with generalized myasthenia gravis (gMG) who have an insufficient clinical response to ongoing, stable standard-of-care therapy.