Abstract Background The containment measures implemented during COVID-19 to curb the virus’s spread disrupted family life globally and profoundly impacted children’s daily behaviours. A decrease in children’s physical activity during COVID-19 is one such health behaviour change that was observed in many European countries. This study aimed to understand the pandemic’s impact on primary school children’s physical activity in Ireland which is important given the epidemic of childhood obesity and chronic diseases in the long term. Methods All Childhood Obesity Surveillance Initiative (COSI) participating countries (n = 45) could voluntarily implement the COVID study as part of their COSI Round 6 (R6) data collection or separately. The parents of First and Second-class primary school children (n = 2,784) who consented to participate in COSI-Ireland R6 were invited to complete the family survey which included the standardised COVID study. The COVID module assessed children’s lifestyles and health behaviours before and during the pandemic through 12 questions. Consenting parents supplied their email or postal address and completed the survey in hardcopy or electronically using LimeSurvey. Descriptive statistics were then calculated on the cleaned pseudonymised dataset (n = 1,060) using IBM SPSS Statistics 27. Results The time spent playing actively outside school hours remained the same for some children on both weekdays and weekends (24.2% and 37.1%, respectively). An increase rather than a decrease in the time spent in active play was also observed among almost twice as many children across Ireland on both weekdays (47.3% and 24.2% respectively), and weekends (40.10% and 21.80% respectively). Conclusions The positive findings show that the public health messaging from the Irish Government which emphasized the importance of staying active during COVID-19 may have been effective. Further research to assess children’s physical activity during COVID-19 is warranted to inform future pandemics. Key messages • In Ireland, unlike in many European countries, a substantial number of primary school children increased their time spent playing actively during the COVID-19 pandemic. • A unique trend in Irish children’s physical activity levels compared to their European counterparts.