Child labor is a pervasive practice; according to the International Labor Organization, there are 160 million child workers worldwide. That figure might, however, greatly underestimate the extent of the issue, since child labor indicators are typically based on surveys with parents – who have no incentive to truthfully disclose that their children work. This, in turn, poses important challenges to the ability of governments and international organizations to monitor and enforce children’s rights. This paper provides first-hand evidence on this issue by combining survey data, based on independent reports from primary school children and their parents in two cocoa-producing regions of Côte d’Ivoire, with novel third-party data from costly certification of cocoa production in these regions, partly based on satellite imagery. We show that adults dramatically under-report child labor in our study sample by a factor of at least 60%. Calibrating a statistical model to account for non-linearity in under-reporting and heterogeneity by local characteristics, we predict the bias-adjusted share of children in employment for each country, and estimate that child labor might affect over 373 million 7-14 year-old children worldwide (95% CI: [~336 million; ~412 million]), nearly 3-fold its global prevalence according to the World Development Indicators. In turn, we document that children self-reports provide accurate regional and aggregate accounts of child labor. Last, evaluating the impacts of a campaign to discourage child labor, we also show that parents’ reports not only underestimate its prevalence, but can even lead to the wrong conclusions about whether and how policy interventions affect child labor.