The aim of this study was to better characterize the moderate intensity of PA among children by applying fuzzy logic as the most appropriate analytical approach. In this perspective, the 6-MWT was selected as a pertinent exercise modality, which covers as a whole, this intensity level.Methodological study.Fuzzy logic was applied to accelerometer output obtained on 46 children aged 9–11 years. A fuzzy subset A was defined from the reference set E using a membership function (degree of truth). To adequately tap the moderate PA, a core of X¯±σ and a support of X¯±2σ (with X¯ the mean, and σ the standard deviation of the distribution) were selected.The walking speed during the exercise averaged 6.1±0.6kmh−1 and the mean HR was 135±14bpm. The movement count (419±127 to 433±148 counts) exhibited no significant changes during the test. A value of 260 counts per 5-s (i.e., 3120cpm) had equally 50% of degree of truth to encompass both “light” and “moderate” intensities of PA. Results suggest that the cut-point of >2296cpm covers a low PA at 100% and a moderate PA at 0%.Fuzzy logic provides a robust basis to processing accelerometer data, and brings a reliable solution to the concern about the in-between of PA intensities. Its application to calibration studies should not support the use of a cut-point of about 2000cpm in children, and linguistic variables should now be preferred to numbered data in defining PA intensities.