This study aims to test two medicines, **ofatumumab** and **siponimod**, against **fingolimod** to see how safe and effective they are for kids with **Multiple Sclerosis (MS)**. MS is a disease where the immune system mistakenly attacks the protective covering of nerves. The study has two parts. The first part lasts 24 months (2 years), where nobody knows which treatment is given to each participant. After that, kids who continue in the study can join the second part, which lasts 60 months (5 years), where everyone knows their treatment. The entire study could last up to 7 years. Kids aged 10-17 with specific MS conditions can join, but those with other immune system diseases or heart problems cannot. The study will have 120 kids, with a few kids aged 10-12 and weighing 40 kg or less. Kids will be checked for at least 6 months after treatment.

• The study can last up to 7 years in total.
• Participants will be randomly assigned to one of three treatment groups.
• Kids must have specific MS conditions to join.