Journal article: In France, as in the US, a mother's labor market participation is influenced by the sex composition of her two eldest siblings. This paper shows that it is also affected by the sex composition of the eldest siblings of the other mothers living in the same close neighborhood. Using the sex composition of neighbors' eldest siblings as an instrumental variable, we identify a significant elasticity of own labor market participation to neighbors' participation. We present supportive evidence by comparing the estimates under two regimes for family benefits (pre- and post-1994 reform) and using quarter of birth as an alternative instrument.