How does the mother’s labour supply affect the household’s demand for childcare? And thus are formal and informal childcare substitutable? In this paper, we address these two questions using micro-data for 14 European countries observed over the period between 2010 and 2017. Relying on a Control Function Approach to account for the endogeneity between childcare and the mothers’ labour supply, we identify different factors affecting the demand for formal and informal childcare. The results show that the mother’s labour supply is a key element in understanding the demand for childcare and suggest that the more the mother participates in the labour market, the higher the household’s demand for childcare services. Moreover, our results support the substitutability hypothesis between formal and informal childcare. Policymakers aiming to promote mothers’ employment should increase the availability of formal childcare services, as this will increase labour supply by mothers and reduce the use of informal care arrangements.