Although armed conflicts and crises affect people of all ages, children are particularly susceptible to the effects of war. One significant consequence of armed conflict that is especially critical for children's well-being, is when the belligerents use tactics specifically focused on harming children, including child soldier recruitment. Despite the increased attention of policy-makers, we still lack systematic knowledge of how many children are directly and indirectly at risk of being recruited by state and non-state actors. In overcoming this gap, we have collected data on the use of children by state and non-state actors from 2010 onwards. Moreover, we estimate the number of children at risk of recruitment. The results of our mapping and estimation sketch a dark picture. According to our estimates, in 2020, approximately 337 million children (or 14%, or more than one in eight of all children globally) were living in a conflict zone with reported child soldier recruitment—that is less than 50 km from ongoing conflict, which involved at least one actor who has been reported to recruit children. We close the paper by taking stock of the current knowledge on the root causes of child soldiering, and we discuss some policy implications.