This paper investigates the relationship between a child's degree of bilingualism and features of parental input. It seeks to demonstrate that parental discourse strategies have a direct bearing on the levels of mixing present in the child's utterances in his weaker language, English. It is based on the longitudinal study of a Catalan/English bilingual child from 1;3 to 4;2 years old. The strategies adopted by both parents in response to their child's mixing are examined following Lanza's (1992, 1997) categorization of parental discourse strategies. Whereas the Catalan-speaking mother negotiates a bilingual context of interaction with her son, as of the child's third year, the English-speaking father endeavours to impose a monolingual context. Such a change of strategy clearly favours the child's increasing use of the minority language, which entails a sharp decline in rates of mixing. It appears that parents' pragmatic choices may have an impact on the development of productive family bilingualism.