The present prospective study investigated a comprehensive model of family stress to explain changes in young children's diet quality from age 3 to 5 years. The direct associations of family stress with child diet quality were examined, as well as the indirect associations via features of the parent–child relationship, including inconsistent parenting practices, negative parent–child interactions, and poor emotional bond. Using an Australian sample of 579 mother–child dyads (child Mage = 3.05 years; 45% boys), higher levels of family stress were predictive of less adequate child dietary quality (i.e., lower fruit and vegetable intake) over time with the effect on fruit intake occurring indirectly via impaired parent–child relationship quality. Notably, it was the relatively less well‐studied indicators of family stress (maternal physical and psychological health difficulties) that were consistently associated concurrently and prospectively with poorer child diet quality. These results provide support for an ongoing broader focus on the family context in which children and parents are embedded, including their exposure to stress, as well as the continued focus on parent–child relationship factors, such as inconsistent parenting practices and negative parent–child interactions, as specific and modifiable predictors of children's diet quality over time.