<p>Family emotional expression is considered one of the key contributors to children’s development and functions as a precondition that is linked with educational equality in the preschool living environment for young children, especially those who live in rural areas. This study explored the family emotional expression of parents who were once left-behind children and its influence on their children’s social–emotional competence (SEC) in less developed areas of western China. A total of 522 families and their children (<i>M</i>_<i>age</i> = 31.86&#xa0;months, <i>SD</i>_<i>age</i> = 5.66; 280 boys, 242 girls) from three rural counties in western China participated in this study. The parents completed the family emotional expression questionnaire, parent impulsivity questionnaire, parent acceptance–rejection questionnaire, and parenting stress scale. Their children took part in the Bayley-III assessment of social–emotional ability. The results indicated that (1) positive family emotional expression enhances children’s social–emotional competence (SEC), whereas negative family emotional expression, parental acceptance and rejection, dysfunctional impulsivity, and parenting stress hinder children’s SEC. (2) Family emotional expression, parenting stress, and children's SEC exhibit significant group differences between left-behind and non-left-behind parents, suggesting the unique challenges faced by children in left-behind families. (3) Parenting stress negatively predicts the development of children’s SEC in both groups, highlighting the detrimental impact of stress on emotional development. (4) In non-left-behind families, positive family emotional expression predicts improvements in children’s SEC, whereas negative emotional expression, parental impulsivity, and rejection negatively affect SEC development.</p>