The recognition that environmental hazards can affect children differently and more severely than adults has provoked growing concern in industrialized nations about the impact of environmental pollution on children's health. In this paper, commissioned by the OECD, we are charged with examining "economic uncertainties" associated with valuing the benefits of environmental policies that reduce risk to children's health. We examine two sources of uncertainty in benefits estimation: forecasting uncertainty and modeling uncertainty. We explore how these sources of uncertainty affect the use of standard economic and non-economic approaches to the valuation of health benefits. These include willingness-to-pay measures, cost-of-illness and human-capital measures, and quality-adjusted life years (QALYs) and related non-economic measures.