Study to Evaluate the Antiviral Efficacy, Safety and Tolerability of Tenofovir Disoproxil Fumarate Versus Placebo in Pediatric Participants With Chronic Hepatitis B Infection

Key Inclusion Criteria: * Male or Female, 2 to \< 12 years of age * Weight ≥ 10 kg * Chronic HBV infection ≥ 6 months * Hepatitis B e antigen (HBeAg)-positive or HBeAg-negative * HBV Viral Load ≥ 100,000 copies/mL * Alanine aminotransferase (ALT) ≥ 1.5 x the upper limit of the normal range (ULN) at screening * Creatinine Clearance ≥ 80 mL/min/1.73m\^2 * Absolute neutrophil count (ANC) ≥ 1,500/mm\^3, hemoglobin ≥ 10 g/dL * Negative pregnancy test at screening * No prior tenofovir DF therapy (participants may have received prior interferon-alfa and/or other oral anti-HBV nucleoside/nucleotide therapy; participants must have discontinued interferon-alfa therapy ≥ 6 months prior to screening; participants experienced on other anti-HBV nucleoside/nucleotide therapy must have discontinued therapy ≥ 16 weeks prior to screening to avoid flare if randomized to the placebo arm) Key Exclusion Criteria: * Pregnant or lactating * Decompensated liver disease * Received interferon therapy within 6 months of screening * Received anti-HBV nucleoside/nucleotide therapy within 16 weeks of screening * Alpha-fetoprotein levels \> 50 ng/mL * Evidence of hepatocellular carcinoma (HCC) * Co-infection with human immunodeficiency virus (HIV), acute hepatitis A virus (HAV), hepatitis C virus (HCV), or hepatitis D virus (HDV) * Chronic liver disease not due to HBV * History of significant renal, cardiovascular, pulmonary, neurological or bone disease * Long term non-steroidal, anti-inflammatory drug therapy Note: Other protocol defined Inclusion/Exclusion criteria may apply