When children learn language, they apply their language-learning skills to the linguistic input they receive. But what happens if children are not exposed to input from a conventional language? Do they engage their language-learning skills nonetheless, applying them to whatever unconventional input they have? We address this question by examining gesture systems created by four American and four Chinese deaf children. The children's profound hearing losses prevented them from learning spoken language, and their hearing parents had not exposed them to sign language. Nevertheless, the children in both cultures invented gesture systems that were structured at the morphological/word level. Interestingly, the differences between the children's systems were no bigger "across" cultures than "within" cultures. The children's morphemes could "not" be traced to their hearing mothers' gestures; however, they were built out of forms and meanings shared with their mothers. The findings suggest that children construct morphological structure out of the input that is handed to them, even if that input is not linguistic in form.