Looking at the earnings profiles of men and women after their first child is born, a number of studies establish that women suffer a larger penalty in earnings than men–a child penalty. Leveraging randomness in the sex of the first birth, we show that the child penalty in the UK is larger when the first born child is a girl. We label this the daughter penalty. Exploiting rich longitudinal survey data, we examine behavioural responses to the birth of a daughter vs. a son to illuminate the underpinnings of the daughter penalty. We find that the birth of a daughter triggers more household specialisation than the birth of a son, with mothers taking on a larger share of household chores and childcare. Mothers suffer a daughter penalty in mental health, while fathers report more satisfaction with their relationship. Our findings imply that girls and boys in the UK are, on average, growing up in different home environments, with girls growing up in households that, by multiple markers, are more gender-regressive. This is potentially a mechanism for the inter-generational transmission of gendered norms.