Abstract Previous research has suggested that the language development of bilingual children benefits from more exposure and opportunities for language use. Typically, this research has used aggregated measures of exposure and use. The role of specific interlocutors and in particular older siblings has received comparatively little attention. In this study, we examine the impact of having an older sibling on the language environment and language development of a group of 31 bilingual Greek–Dutch toddlers aged 16 to 30 months growing up in the Netherlands. Approximately half (n = 14) of the toddlers had an older sibling. With respect to language environment, toddlers with older siblings were in general found to hear and use more Dutch at home than their first-born peers. There were however no differences between the two groups of toddlers in terms of parental language use. With respect to language development, toddlers with older siblings were found to score higher than first-born peers on measures of Dutch receptive vocabulary, productive vocabulary, and morphosyntactic complexity. For Greek, no such differences were observed. The findings are discussed in light of factors including family constellation, parental language proficiency, bilingual parenting strategies, and the wider sociolinguistic context.