Both perceptual mechanisms (e.g., threat detection/avoidance) and social mechanisms (e.g., fears fostered via negative media) may explain the existence of the uncanny valley; however, existing literature lacks sufficient evidence to decide whether one, the other, or a combination best accounts for the valley's effects. As perceptually oriented explanations imply the valley should be evident early in development, we investigated whether it presents in the responding of children ( N=80; ages 5-10) to agents of varying human similarity. We found that, like adults, children were most averse to highly humanlike robots (relative to less humanlike robots and humans). But, unlike adults, children's aversion did not translate to avoidance. The findings thus indicate, consistent with perceptual explanations, that the valley effect manifests well before adulthood. However, further research is needed to understand the emergence of the valley's behavioral consequences.