This study is about testing two medicines, ofatumumab and siponimod, against another medicine called fingolimod for children with a disease called Multiple Sclerosis (MS). MS is a condition where the body’s defense system mistakenly attacks the brain and spine. The study is for kids aged 10 to 17 years old and lasts up to 7 years, with two parts: Core Part (first 2 years) and Extension Part (next 5 years). During the Core Part, neither the doctors nor the kids will know which medicine they're getting to make sure results are fair. The Extension Part is mostly open, meaning the kids will know what they're taking. To be part of the study, kids must have MS and be between 10 to 17 years old. Kids with diseases affecting the immune system, severe heart or kidney problems, or progressive MS cannot join.

• Study lasts up to 7 years.
• Participants needed: 120 children with MS.
• Some visits and tests required, but no cost to participants.