BackgroundReduced physical activity (PA) is associated with childhood obesity and is a target for intervention. This study aimed to assess objectively measured PA patterns in Dutch children across weight categories, age groups and gender at the start of a lifestyle intervention.Methods202 children with overweight and (morbid) obesity (55% girls, 12 ± 3y of age, BMI z-score + 3.15 ± 0.73), referred to the Centre for Overweight Adolescents and Children’s Healthcare (COACH, Maastricht UMC+) were included. Children were categorized as overweight, obese or morbidly obese according to their BMI z-score. PA was measured with the GT3X Actigraph accelerometer.ResultsPA levels in children with morbid obesity were higher compared to children with obesity, also after correction for age and gender (corrected difference (B) 118 counts per minute (cpm), p = .006). Sedentary behaviour (SB) was lower in children with morbid obesity compared to children with obesity (B -51 min/day, p = .018). Girls performed significantly less moderate to vigorous PA than boys (B -11 min/day, p < .001) and with increasing age, children performed less PA (B -46 cpm, p < .001) and SB increased (B 18 min/day, p < .001).ConclusionWeight category morbid obesity, lower age and male gender were positively associated with PA and negatively with SB. These findings highlight the need for tailored PA promotion.Trial registration: The trial is registered with Clinicaltrials.gov NCT02091544. Registration date: March, 19th, 2014. (https://clinicaltrials.gov/ct2/show/NCT02091544?term=NCT02091544&draw=2&rank=1)