Analyzing the development of the noun-to-verb ratio in a longitudinal corpus of four Chintang (Sino-Tibetan) children, we find that up to about age four, children have a significantly higher ratio than adults. Previous cross-linguistic research rules out an explanation of this in terms of a universal noun bias; instead, a likely cause is that Chintang verb morphology is polysynthetic and difficult to learn. This hypothesis is supported by the fact that the development of Chintang children's noun-to-verb ratio correlates significantly with the extent to which they show a similar flexibility with verbal morphology to that of the surrounding adults, as measured by morphological paradigm entropy. While this development levels off around age three, children continue to have a higher overall noun-to-verb ratio than adults. A likely explanation lies in the kinds of activities that children are engaged in and that are almost completely separate from adults' activities in this culture. © Copyright Cambridge University Press 2011.