Abstract While numerous studies have recently shown that variation in input quantity predicts children’s rate of acquisition across a range of language skills, comparatively little is known about the impact of variation in input quality on (bilingual) children’s language development. This study investigated the relation between specific quality-oriented properties of bilingual children’s input and measures of children’s language development across a number of skills while at the same time taking family constellation into account. Participants were bilingual preschoolers (n = 50) acquiring Dutch alongside another language. Preschoolers’ receptive and productive vocabulary and morphosyntax in Dutch were assessed. Parental questionnaires were used to derive estimates of input quality. Family constellation was first operationalized as presence of a native-speaker parent and subsequently in terms of patterns of parental language use. Results showed that proportion of native input and having a native-speaker parent were never significant predictors of children’s language skills, whereas the degree of non-nativeness in the input, family constellation in terms of parental language use, and language richness were. This study shows that what matters is not how much exposure bilingual children have to native rather than non-native speakers, but how proficient any non-native speakers are.