This study contributes to the emerging research on children’s well-being during the COVID-19 pandemic. The objectives are threefold. Firstly, we compare the life satisfaction of children in the COVID-19 pandemic with that before the pandemic. Secondly, we assess how the COVID-19 pandemic affected the importance of social support regarding children’s life satisfaction. Thirdly, we investigate if the COVID-19 pandemic has impacted boys’ and girls’ life satisfaction differently. Data from children aged between 9 and 12 in Flanders (Dutch speaking part of Belgium, n = 3289) from two waves of ISCWeB (International Survey of Children’s Well-Being) show that life satisfaction of boys and girls decreased between 2018 (pre-COVID-19 pandemic) and 2021 (during COVID-19 pandemic). Moreover, we find that during the COVID-19 pandemic social support gained importance as a predictor of children’s life satisfaction. This change in the predictive power of social support, however, turns out to be source- and gender-dependent. We find that, for both boys and girls, the importance of social support from the nuclear family on life satisfaction increased most. Friends also became a more important predictor of life satisfaction during the pandemic for both boys and girls. With respect to support from teachers we find a clear gender difference. During the pandemic, support from teachers became more important for boys but not for girls. In general, our findings suggest that to combat the negative consequences of future health crises on children’s well-being, initiatives should focus on providing children with multiple and diverse sources of social support.