With the increasing rate of mental health disorders among youth in the United States (U.S.) and the essential role of parents in children’s development, many studies have investigated the relationship between parental factors and children’s mental health. The current study expanded on this research by exploring the impact of parent solid self (i.e., one subcategory of differentiation of self), parenting stress, parenting styles, and parent involvement in treatment on children’s mental health symptom severity. The sample included 216 parents (U.S. residents; Mage = 33.84, SDage = 5.384) with at least one youth aged 3–17 years actively or historically in mental health treatment. Participants completed an online survey that included a demographic questionnaire and measures of parenting styles, parental solid self, parental stress, and children’s symptom severity. A simple linear regression found that parental solid self and stress levels were associated with the severity of children’s symptoms. A two-way ANOVA revealed that parenting styles had a significant main effect on children’s symptom severity. Results also showed that the level of authoritative parenting style mediated the relationship between parental solid self and children’s symptom severity. This study further highlighted the importance of promoting individual therapy or psychoeducation for parents and how it might benefit children’s treatment. Future research may consider children’s perspectives, how parents engage with their child’s treatment, incorporating more expansive assessment methods, and longitudinal designs to further explore the impact of parents’ differentiation of self, parental stress, parenting styles, and parental involvement in treatment on children’s symptom severity.