This is a multi-center, open-label single-arm study to investigate the pharmacokinetics and safety of tocilizumab (RoActemra/Actemra) in participants less than 2 years old with active sJIA. Participants will receive tocilizumab infusions every 2 weeks. The anticipated time on study treatment is 12 weeks (Main evaluation period). Participants will have the option to continue tocilizumab treatment until participant reaches 2 years of age or up to one year from baseline, whichever is longer. An optional extension period will follow the main evaluation period.