This study will evaluate the efficacy and safety of erenumab in migraine prevention in children (6 to \<12 years) and adolescents (12 to \<18 years) with episodic migraine. The study hypothesis is that in pediatric participants with episodic migraine, the combined erenumab dose group has a greater reduction from baseline to week 9 through week 12 (month 3) in monthly migraine days (MMDs) when compared with placebo in the double-blind treatment phase (DBTP).