More than 1 in 10 children worldwide are affected by armed conflict. The effects are both direct and indirect and are associated with immediate and long-term harm. The direct effects of conflict include death, physical and psychological trauma, and displacement. Indirect effects are related to a large number of factors, including inadequate and unsafe living conditions, environmental hazards, caregiver mental health, separation from family, displacement-related health risks, and the destruction of health, public health, education, and economic infrastructure. Children and health workers are targeted by combatants during attacks, and children are recruited or forced to take part in combat in a variety of ways. Armed conflict is both a toxic stress and a significant social determinant of child health. In this Technical Report, we review the available knowledge on the effects of armed conflict on children and support the recommendations in the accompanying Policy Statement on children and armed conflict.