Embodied theories of language comprehension propose that readers construct a mental simulation of described objects that contains perceptual characteristics of their real-world referents. The present study is the first to investigate directly whether implied object size is mentally simulated during sentence comprehension and to study the potential influence of developmental factors on mental simulation by comparing adults' and children's mental simulation processing. Participants performed a sentence-picture verification task in which they read a sentence that implied a large or a small size for an object and then saw a picture of the object that matched or mismatched the implied size. Responses to pictures were faster when implied size and pictured size matched, suggesting that readers activated perceptual information on object size during sentence comprehension. The magnitude of the match effect was equal across age groups. The results contribute to refining and advancing knowledge with respect to the nature of mental simulations.