Immigrant children who faced forced separation from their parents may be at heightened risk of developing mental health disorders, including depression, post-traumatic stress disorder (PTSD), and anxiety disorders. This cross-sectional study assessed the mental health of children being held in U.S. immigration detention who had been previously separated from their mothers. We interviewed 73 mothers about their eldest child age 5-17 using the Parent-Report version of the Strengths and Difficulties Questionnaire (SDQ). Among these children, many had elevated scores for emotional problems (49%), peer problems (21%), and total difficulties (15%). Male children demonstrated significantly higher rates of abnormal peer problems compared to females. Younger children (age 5-11 years) also demonstrated significantly higher rates of abnormal conduct problems, hyperactivity, and total difficulties. Scores did not differ significantly based on length of separation. Results reveal that children who had been separated from their parents experience high levels of mental health distress, which are especially high in younger children. Regardless of length of separation, these children would benefit from comprehensive mental health treatment with a culturally-responsive and trauma-informed lens.