Background: Child growth impairment (GI) causes much psychological, physical and economic harm to the community while a healthy growth and development at early childhood ensures access to a healthy society. Objectives: This study aimed to evaluate the factors affecting GI of children under 6 years of age by using marginal models in West Azerbaijan Province, Iran. Methods: In this longitudinal cohort study, 1070 children below 6 years were in a two-stage cluster sampling randomly selected and studied. The growth characteristics of the studied children (height, weight) and their development features (walking, speaking and teething age) were recorded, during a 6-year follow-up. Data were collected by R statistical software and analyzed by using independent marginal model. Results: The results of this study showed that maternal age at the time of birth (P = 0.001) also her educational level (P < 0.05) and occupational status (P = 0.000), birthing method (P = 0.001), child's gender (P = 0.000), breastfeeding (P = 0.000) and child's walking age (P = 0.000) had a significant effect on GI. Conclusions: Present study revealed that the demographic factors and child's walking age have a significant effect on children's GI. At early childhood, GI influences many domains of individual's life and subsequently the society status. So, it is recommended that the determinants of this crucial threat to be identified and effective plans to be provided for any problems that may arise at this time.