Abstract Research indicates that the uptake of formal childcare for children under age 3 is lower among migrant origin parents than among native parents in most European countries, and that these differentials extend to the second generation. Despite considerable investments in formal childcare availability in many European countries, it remains unclear whether and to what extent expanding local childcare availability effectively diminishes migrant-native uptake differentials due to the lack of longitudinal research. Therefore, this study assesses for Belgium to what extent expansions in childcare availability within municipalities in the period 2010–2014 has increased the uptake of formal childcare for children under age 3 among households where the mother has a second generation Southern European, Maghreb or Turkish background, versus no migration background. We use longitudinal census and register data for Belgium that were linked to longitudinal tax return data on childcare expenses and municipality-level data on childcare availability for children aged 0–3. Our results show that Southern European and Turkish origin mothers become more likely to use formal childcare when childcare places become more widely available within their municipalities, but also that the uptake gap with native mothers persists, since there is no differential effect of increasing local childcare availability. Since local childcare expansions entail a slightly stronger increase in formal childcare uptake among Maghreb origin mothers compared to native mothers, this results in slightly decreasing migrant-native uptake gaps, although considerable uptake gaps remain. To our knowledge, this is the first longitudinal study addressing the relationship between local childcare availability and uptake differentials by migration background. This study can inspire avenues for follow-up research which could provide additional insight into the possible mechanisms behind the varying effects of increasing local childcare availability by migration ...