Hepatitis B virus (HBV) is endemic in Africa, where it may occur as an HIV coinfection. Data remain limited on HIV–HBV epidemiology in Africa, particularly in children. Using programmatic data from pediatric HIV clinics in Lusaka, Zambia during 2011–2014, we analyzed the prevalence of chronic HBV coinfection (defined as a single positive hepatitis B surface antigen [HBsAg] test) and its impact on immune recovery and liver enzyme elevation (LEE) during the first year of antiretroviral therapy. Among 411 children and adolescents, 10.4% (95% confidence interval, 7.6–14.1) had HIV–HBV. Coinfected patients were more likely to have World Health Organization stage 3/4, LEE and CD4 <14% at care entry (all p < 0.05). During treatment, CD4 increases and LEE incidence were similar by HBsAg status. HBsAg positivity decreased (11.8% vs. 6.6%; p = 0.24) following HBV vaccine introduction. These findings support screening pediatric HIV patients in Africa for HBV coinfection. Dedicated cohorts are needed to assess long-term outcomes of coinfection.