This study aimed to assess the relative impact of the home food environment on children’s diet after the introduction of a new supermarket in a food desert. This study builds upon a natural experiment to longitudinally examine the food-purchasing behaviors and diets among a randomly selected population of households in two major Pittsburgh food desert neighborhoods, one of which underwent a transformation by obtaining a full-service supermarket in 2013. Parental diet was assessed before and after the opening of the supermarket. The home environment and children’s intake of fruits and vegetables was measured only after the store’s opening. Structural equation modeling was used to estimate the pathways between changes in parental dietary quality at follow-up and children’s dietary intake through the home environment. The study found that parental dietary improvement after the supermarket was opened was indirectly and positively associated with children’s healthy dietary behaviors through family nutrition and physical activity patterns.