The question of how children learn what words mean is one that has long perplexed philosophers and psychologists. As Quine famously pointed out, the problem of accounting for word learning is a deep one: simply hearing a word uttered in the presence of an object tells a learner next to nothing about its meaning. Yet somehow, children learn to understand and use words correctly. How? Here, we find that learning theory offers an elegant solution to this seemingly intractable puzzle in language acquisition. To test its predictions, we administered an ambiguous word-learning task to toddlers, undergraduates and developmental psychologists. Intriguingly, while the toddlers’ performance was consistent with our hypothesis – and with the workings of general learning mechanisms that would facilitate verbal acquisition – adult performance differed markedly. These results have implications both for how adult intutions inform the study of early language learning and for problems in second-language acquisition.