Adverse shocks can create inequalities if some groups respond more strongly than others. This paper examines whether a common disruption leads to differential changes in children’s subjective well-being by gender. We use longitudinal data from the Luxembourg Child Well-Being Survey, which follows the same children before (2019) and after (2021) the COVID-19 shock, a major disruption to schooling, social interactions, and daily routines. Using fixed-effects models, we estimate within-child changes in life satisfaction, positive affect, and negative affect. Girls and boys report similar levels of life satisfaction and positive affect before the disruption, but follow different trajectories afterward. Girls experience larger declines in life satisfaction and positive affect and a larger increase in negative affect, with the sharpest deteriorations concentrated in school experiences, family relationships, self-perceptions, and loneliness. As a result, a sizeable gender gap in subjective well-being emerge, which increases with age and remains robust to alternative specifications, selective attrition, and alternative cardinalizations of ordinal well-being scales. The gender gap is not concentrated among specific socio-economic groups.