Background: Childhood obesity is a major health concern. Caregivers' feeding practices are modifiable targets of obesity prevention. The study tested two hypotheses: (1) autonomy-promoting feeding practices are associated with lower BMI; and (2) diet mediates the association. We also explored examined whether feeding practices and BMI z-score (BMIz) associations are moderated by child sex, caregiver race, education, family poverty level, and food insecurity. Methods: Cross-sectional study of 437 preschoolers (44.4% girls, 38.2% Black/Other, mean age 48.1 months) and caregivers (90.2% female) from 50 child care centers. Feeding Practices were measured by Comprehensive Feeding Practices Questionnaire, child-size perception by preschooler silhouettes, temperament by the Behavior Rating Inventory of Executive Function, child diet by Young Children Food and Drink Questionnaire, and BMIz by measured weight and height. Latent profile analysis delineated feeding practice patterns. Structure equation modeling assessed the patterns in relationship to BMIz. Mediation and multiple-group analyses were used to assess mechanisms of feeding practice patterns and BMIz association. Results: From the three feeding practice patterns, Controlling, Balancing, and Regulating, Regulating was associated with lower child BMIz (b = -0.09) compared to Controlling. Higher difficult temperament (b = 0.09), higher caregiver BMIz (b = 0.26), and caregiver desire for thinner (b = 0.23) were associated with BMIz (p < 0.05). Evaluations of moderators and mediators were not significant. Conclusions: Comprehensive feeding practices support family factors related to child BMIz. Longitudinal research is needed to examine temporal associations between feeding practices and BMIz, with attention to autonomy-supporting practices, promotion of young children's self-regulation, and caregivers' perceptions of child temperament and size. Trial Registration: NCT03111264.