Introduction. Successful prevention of mother-to-child transmission (PMTCT) of the human immunodeficiency virus (HIV) requires early diagnosis, consistent access to antiretroviral therapy (ART), and regular health care during and after pregnancy. This study assessed the determinants of early HIV diagnosis by children born to HIV-positive (HIV+) mothers in the Kongo Central Province, Democratic Republic of the Congo (DRC). Methodology. Data from 230 HIV+ mothers screened under the PMTCT program between July 2015 and December 2017 were extracted from the databases of 31 Health Zones (HZ) of Kongo Central province. Data detailing laboratory and anthropometric findings, morbidity, and mortality were collected from each exposed child. The determinants of inaccessibility to early diagnosis were identified using logistic regression. Results. The mothers' mean age was 32.4 years, and 90.9% were on ART; 68.8% of children were older than 12 months at diagnosis. Diagnosis during the first 6 months of the child's life was critical. Malnutrition was found in almost 90% of the children. Determinants of non-access to an early diagnosis were mothers who attained a primary education level and did not disclose their HIV status. Conclusion. All possible interventions should be considered to prevent mother-to-child HIV transmission. To ensure a child's survival to their first birthday, early diagnosis should be performed soon after birth to an HIV+ mother and ART should be initiated.