Previous research has identified food insecurity as a risk factor for obesity but those studies employed cross-sectional designs and were largely focused on adults and young children. In addition, there is a paucity of studies examining the association between food insecurity and changes in children's overall diet quality. This study aimed to assess whether food insecurity is associated with subsequent changes in diet quality and BMI z-scores over 2 years among 7- to 12-year-old children. We used 2011-2019 secondary data ( = 404) from three randomized controlled trials in Minnesota. Food insecurity was identified using the U.S. Household Food Security Survey Module at baseline (Time 0). Diet quality was determined using the Healthy Eating Index (HEI)-2015 from 24-hour recalls, and BMI z-scores were calculated using measured height and weight. These two outcomes were measured at Time 0, Time 1 (10-12 months from Time 0), and Time 2 (15-24 months from Time 0). Compared with children from food-secure households, those from food-insecure households experienced a 0.13 greater increase in BMI z-scores from Time 0 to Time 2 [95% confidence interval (CI): 0.04 to 0.21] and a 4.5 point increase in HEI-2015 from Time 0 to Time 1 (95% CI: 0.99 to 8.01). Household food insecurity may widen weight disparities among elementary school-aged children. Further studies are needed to identify the role of diet quality in weight changes among children with food insecurity. Clinical Trial Registration Number: NCT01538615, NCT02029976, NCT02973815.