Background: The COVID-19 pandemic imposed social isolation measures, which impacted the child population, especially regarding physical and mental health aspects. Purpose The aim of this study was to investigate the relationship between sedentary behavior, cardiorespiratory fitness, immunoglobulin -A secretion, and anxiety symptoms in 267 children aged 6-11 years, eutrophic or overweight. Methods: Sedentary behavior was evaluated by the time of exposure to screens. Cardiorespiratory fitness was assessed using the 6-minute run/walk test and immunoglobulin-A by salivary samples. Anxiety symptoms were reported by the SCAS-version for parents. Results: It was observed that after a period of confinement, overweight in children had a negative impact on cardiorespiratory performance and sedentary behavior. Differences were also observed in the concentration and secretion rate of SIgA in the overweight group compared to the normal weight group. Discussion: The return to face-to-face classes brought a high proportion of overweight students, who showed lower aerobic performance. Considering sedentary behavior, all groups presented values greater than 2 hours of daily exposure to screens. Translation to Health Education Practice: Special attention is needed from health professionals and teachers in relation to reducing sedentary behavior and improving cardiorespiratory fitness in schoolchildren.