This placebo-controlled study evaluates the efficacy, safety and tolerability of tenofovir disoproxil fumarate (TDF) in participants 2 to < 12 years old with chronic Hepatitis B infection. While studies have shown significant virologic response in adults and adolescents, the effect in children is not well established. This study will provide valuable data that can help establish the efficacy and safety profiles of TDF in children. The study will consist of 72 weeks of blinded randomized treatment, after which participants will switch to open-label TDF treatment for an additional 120 weeks.