Vision-for-action and vision-for-perception both rely on shape representations derived within the visual system. Whether the same psychological and neural mechanisms underlie both forms of behavior remain hotly contested and whether this arrangement is equivalent in adults and children is controversial, as well. To address these outstanding questions, we utilized an established psychophysical heuristic, Weber's law, which, in adults, has typically been observed for perceptual judgment tasks but not for actions such as grasping. We examined whether this perception-action dissociation in Weber's law was present in childhood as it is in adulthood and whether it was modulated by stimulus complexity. Two major results emerged. First, although adults evinced visuomotor behavior that violated Weber's law, young children (4.5-6.5 years of age) adhered to Weber's law when they grasped complex objects (Efron blocks), which varied along both the graspable and non-graspable dimensions to maintain a constant surface area, but not when they grasped simple objects, which varied only along the graspable dimension. Second, adherence to Weber's law was found across all ages in the context of a perceptual task. Together, these findings suggest that in early childhood, visuomotor representations are modulated by perceptual representations, particularly when a refined description of object shape is needed.