Previous studies have suggested that advertising exposure affects materialism among youth. However, this causal effect has not been investigated among children in middle childhood, who are in the midst of consumer development. Furthermore, the mechanism underlying this relation has not been studied. To fill these lacunae, this study focused on the longitudinal relation between children’s television advertising exposure and materialism. We investigated advertised product desire as a mediating variable. A sample of 466 Dutch children (ages 8-11) was surveyed twice within a 12-month interval. The results show that advertising exposure had a positive longitudinal effect on materialism. This effect was fully mediated by children’s increased desire for advertised products.