Objective A growing number of youth are utilizing digital mental health interventions (DMHIs) for treatment of mental health problems such as anxiety, depression, and ADHD. Although these mental health symptoms are closely related to sleep problems, it is unknown whether nonsleep DMHIs indirectly confer improvements in sleep. Using retrospective data, the current study assesses (1) whether youth sleep problems improve over participation in a nonsleep DMHI, and (2) whether mental health symptom severity and improvement are correlated with sleep problem severity over time. Methods Sleep problems and mental health symptoms were assessed every 30 days among children (ages 5–12) and adolescents (ages 13–17) participating in a pediatric digital mental health intervention (DMHI; N = 1219). Results Children and adolescents with elevated sleep problems (39.3%; n = 479) were older (P < .001), more predominantly female (P < .001), and more likely to have elevated anxiety (P < .001), depressive (P < .001) and inattention symptoms (P = .001), as compared to those with nonelevated sleep problems (60.7%; n = 740). From the baseline to last assessment, 77.3% (n = 269) of members with elevated sleep problems exhibited improvements, with sleep problems decreasing significantly over each month in care (P < .001). Members with improvements in anxiety, depressive, and/or ADHD symptoms had larger improvements in sleep over time compared to their peers with no improvement in their mental health symptoms (Months in care*Change type: P < .001 for all). Conclusions Our results provide preliminary evidence that participation in a pediatric DMHI is associated with improvements in sleep problems, even when youth are not being treated directly for sleep problems. These findings highlight a valuable secondary benefit of participating in mental health care within pediatric DMHIs and warrant further experimental research.