Study to Assess the Long-term Safety of Dupilumab Administered in Participants ≥6 Months to <18 Years of Age With Atopic Dermatitis (AD)

The primary objective of the study is to assess the long-term safety of dupilumab in pediatric participants with AD. The secondary objectives of the study are: * To assess the long-term efficacy of dupilumab in pediatric participants with AD * To assess the trough concentrations of functional dupilumab in serum and the immunogenicity in pediatric participants with AD after re-treatment with dupilumab Optional Pre-filled Pen (PFP) Sub-Study in pediatric patients ≥2 to \<12 years of age with AD Co-Primary Objectives are: * To evaluate the pharmacokinetic (PK) of dupilumab PFPs * To evaluate the safety of dupilumab PFPs Secondary Objective is: \- To evaluate the immunogenicity of dupilumab PFPs