Introduction: Retention in care and reengagement of lost to follow-up (LTFU) patients are priority challenges in pediatric HIV care. We aimed to assess whether a telephone-call active tracing program facilitated reengagement in care (RIC) in the Manhiça District Hospital, Mozambique. Methods: Telephone tracing of LTFU children was performed from July 2016 to March 2017. Both ART (antiretroviral treatment) and preART patients were included in this study. LTFU was defined as not attending the clinic for ≥120 days after last attended visit. Reengagement was determined 3 months after an attempt to contact. Results: A total of 144 children initially identified as LTFU entered the active tracing program and 37 were reached by means of telephone tracing. RIC was 57% (95% CI, 39–72%) among children who could be reached versus 18% (95% CI, 11–26%) of those who could not be reached (p = 0.001). Conclusion: Telephone tracing could be an effective tool for facilitating reengagement in pediatric HIV care. However, the difficulty of reaching patients is an obstacle that can undermine the program.