## 1 Introduction  
In March 2020, the World Health Organization (WHO) declared the outbreak of Coronavirus Disease (COVID-19) a global pandemic affecting more than 130 countries [1]. To slow the spread and reduce transmission rates, governments around the world imposed various measures--requiring the closure of many institutions, programmes, facilities, and other community spaces--and imposed limitations on the public use of outdoor community spaces. These restrictions caused a decrease in the frequency and duration of physical activity and outdoor activity, while recreational screen use increased significantly [2]. Additionally, habits related to sleep were affected, with changes in the duration, timing, and quality of sleep [2]. The widespread impact on health-related behaviours has caused a decline in adherence to the 24 h movement guidelines [2].  
The 24 h movement guidelines for preschoolers, children, and adolescents shift the focus from individual activity components for preschoolers, children, and adolescents' health promotion by integrating all 24 h movement behaviours. In accordance to these guidelines, throughout the day (24 h), preschoolers should do at least 180 min of a variety of types of physical activity (PA; of which at least 60 min/day is moderate-to-vigorous PA), and both children and adolescents should do an average of 60 min/day of moderate to vigorous PA, have \(<\)1 h/day(for preschoolers) or \(\leq\)2 h/day (for both children and adolescents) of recreational screen time (ST), and get 10 to 13 h (age range 3-4 years old), 9 to 11 h (age range 5-13 years old), or 8 to 10 h (age range 14-17 years old) of sleep per day [3]. Meeting overall 24 h movement guidelines has been reported as being associated with better overall health [4; 5; 6; 7]. A global systematic review [8] reported that only 7.2% of children and adolescents follow the mentioned 24 h recommendations. This already-low prevalence seems to have been further exacerbated by the COVID-19 pandemic, as indicated in a recent scoping review [2]. The review concluded that the COVID-19 pandemic was associated with adverse changes in the quantity and nature of physical activity, sedentary behaviour, and sleep among children and adolescents [2].  
Health-related quality of life (HRQoL) is known as the level of well-being reported through the assessment of different dimensions of life, reflecting the influence that these dimensions have on health status; characterised as subjective, multidimensional, and changing over the years [9]. HRQoL is recognised as a relevant construct with multiple dimensions of a youth's physical, mental, emotional, and social functioning, and can be considered as an indicator of general health [10]. The assessment of HRQoL in children and adolescents is crucial, since those with low HRQoL in childhood are less likely to follow a healthy trajectory later in life [11].  
To our knowledge, few studies have examined the association between complying with the 24 h movement guidelines and HRQoL among children and adolescents, and all were conducted prior to the COVID-19 pandemic [4; 5; 12]. During the COVID-19 pandemic, [PERSON] et al. (2021) [13] developed a systematic review indicating that the pandemic has had negative consequences on the HRQoL of children and/or adolescents. However, there is no research examining the associations between 24 h movement guidelines and HRQoL throughout the COVID-19 pandemic. Thus, the present study aimed to examine the association between compliance with all the 24 h movement guidelines and HRQoL during the COVID-19 pandemic in children and adolescents.