Validity of the Movement Behavior Questionnaire-Child (MBQ-C) Physical Activity Domain among Toddlers.

Background: The Movement Behavior Questionnaire-Child (MBQ-C) is a caregiver-reported tool designed to assess 24-hour movement behaviors (physical activity [PA], sleep, and screen time) in children under age 5 years who are able to walk. This study evaluated the test-retest reliability and convergent validity of the MBQ-C PA domain among toddlers aged 1-2 years. Method: This ancillary study was conducted within the Child and Mother Physical Activity Study (CAMPAS), a longitudinal cohort examining early childhood PA development. Toddlers aged 1-2 years wore an ActiGraph wGT3X-BT accelerometer on the hip for 7 consecutive days. Mothers completed the MBQ-C PA domain twice, once before and once after the wear. The domain included four items assessing time spent in active play (categorical responses from 0 minutes to > 4 hours per day) and energetic play (categorical responses from 0 minutes to > 2 hours per day) on a typical weekday and weekend day. Responses were converted to minutes per day using the midpoints of categorical ranges. Test-retest reliability was evaluated using intraclass correlation coefficients (ICCs). Convergent validity was examined using Spearman correlations between MBQ-C-derived and accelerometer-derived PA metrics. Results: A total of 71 toddler-mother dyads were included in analysis (child age = 24 ± 4 months; range = 16-34 months). The proportions of respondents reporting "0 minutes" on the four MBQ-C PA items ranged from 0-10%. No respondents reported the highest response to any MBQ-C PA items, indicating no to minimal floor and ceiling effects. Accelerometer-derived mean acceleration was 21.0 ± 4.5 mg. Accelerometer-derived total PA and moderate- and vigorous-intensity PA were 245 ± 42 and 79 ± 23 minutes/day, respectively. Test-retest reliability was poor for active play (ICC = 0.45; 95% CI = 0.20, 0.64) and moderate for energetic play (ICC = 0.57; 95% CI = 0.38, 0.76), respectively. MBQ-C-derived PA estimates were not correlated with accelerometer-derived PA estimates (ρ=-0.18 to 0.07; all p > 0.05). Conclusion: Among toddlers aged 1-2 years, the MBQ-C PA domain demonstrated poor to moderate test-retest reliability and very low convergent validity relative to accelerometer-derived PA measures. These findings underscore the challenges of accurately capturing toddlers' PA through caregiver report, given the highly sporadic and unstructured nature of movement at this age.