Background: The COVID-19 pandemic has accentuated sedentarism in children, including those with autism. Given the importance of the topic for long-term health, this study aimed to explore the post-pandemic relationship between physical activity, sedentary behaviours and quality of life (QOL) in children with autism from Romania and Greece. Methods: An online questionnaire collected information regarding physical activity levels in children and their parents, children's sedentary behaviours and QOL from 83 Romanian parents (m1[subscript age] = 40.1; sd1[subscript age] = 6.37) and 42 Greek parents (m2[subscript age] = 39.5; sd2[subscript age] = 5.45) between March and July 2022. age age age age Results Most Greek children (95%) had 2 or 3 weekly hours of physical education at school/kindergarten, while only 64% of Romanian children had the same level of physical education. Romanian parents reported being more active (X[superscript 2][subscript weekdays]= 33.7, df = 3, p < 0.001; (X[superscript 2][subscript leisure]= 41.8, df = 2, p < 0.001) than the Greek counterparts. Contrary to expectations, the parents' physical activity did not correlate with the child's physical activity. Sedentary behaviour time was significantly higher in Greek than Romanian children during working days and the weekends. Sedentary behaviour during weekdays predicted the child' QOL. Conclusions: This exploratory study offers insight into Romanian and Greek children's patterns of physical and sedentary activities. The results stress the need to increase physical activity and decrease sedentary behaviours in children with autism from Romania and Greece. The practical implications and limits of this exploratory approach were further discussed.