Object substitutions in play (e.g. using a box as a car) are strongly linked to language learning and their absence is a diagnostic marker of language delay. Classic accounts posit a symbolic function that underlies both words and object substitutions. Here we show that object substitutions depend on developmental changes in visual object recognition: 18- to 30-month old children (n = 63) substitute objects in play after they have developed the adult-like ability to recognize common objects from sparse models of their geometric structure. These developmental changes in object recognition are a better predictor of object substitutions than language or age. A developmental pathway connecting visual object recognition, object name learning, and symbolic play is proposed in which object substitutions are like the canary in the coal mine: they are not causally related to language delay, but their absence is an easily detected signal of a problem in language acquisition.