Background and Objective:
The COVID-19 pandemic and related restrictions may have modified children’s health behaviours with varying effects according to social circumstances. We aimed to assess the demographic and socio-economic determinants of health behaviours and their changes during the pandemic.

Methods:
A population-based sample of children (3-17 years) was recruited between December 2021 and June 2022 in Geneva, Switzerland. Screen time (ST), physical activity (PA), green space time (GST), sleep time, and their pandemic-related changes were parent-reported. Adherence to international recommendations for health behaviours was defined using age-specific thresholds (tertiles for GST), and determinants evaluated with generalized estimating equations.

Results:
Of 2067 children (49% female; mean age=10.2), 68% met the recommendations for ST and PA, and 80% for sleep time. Girls and older children were more likely not to meet PA (Odds Ratio=1.88; 95% Confidence Interval: 1.55-2.27, OR=1.11, 95%CI: 1.08-1.14, respectively) and sleep guidelines (OR=1.29; 95%CI: 1.02-1.63, OR=1.09, 95%CI: 1.05-1.12, respectively), and to have low GST (OR=1.43; 95%CI: 1.19-1.72, OR=1.18, 95%CI: 1.15-1.21, respectively); age was also associated with excessive ST (OR=1.53; 95%CI: 1.46-1.62). Children whose parents were born in Southern/Eastern-Europe or outside Europe, or had a lower education were at increased risk of not meeting ST and sleep recommendations. During the pandemic, older age and an average-to-poor financial situation were associated with unhealthy behavioural changes including increased ST, and decreased PA and GST, but also with sleep quality improvement. Decrease in PA and GST was also more likely among children from Southern/Eastern- or non-European origin, or whose parents had a lower education.

Conclusion:
Older age, migration background and lower socio-economic conditions were determinants of unhealthy behaviours and of a worsening of behaviours during the pandemic, although positive effects were also observed. The pandemic may have reinforced existing social patterning of health behaviours, which calls for tailored interventions targeting specific subgroups.