Epidemiological literature on children's mental health and children's adverse childhood experiences (ACEs) have consistently pointed to widespread, unaddressed, and treatable high-risk conditions among children. To estimate the proportion of children with either high levels of ACEs and/or high levels of mental health symptoms who were not receiving services from behavioral health professionals. This cross-sectional study included 11 896 children who participated in 3 National Surveys of Children's Exposure to Violence (NatSCEV), which were nationally representative surveys conducted in 2008, 2011, and 2014. The surveys entailed telephone interviews with youth aged 10 to 17 years and caregivers of children aged 2 to 9 years. Data were analyzed from February to August 2020. Nationally representative samples were obtained from a mix of random digit dial and address-based sampling methods. The primary outcome was the proportion of children with high ACEs, high distress symptoms, and both who were receiving clinical contact, broken down by demographic characteristics. Of the 11 896 children, 4045 (34.0%) participated in the 2008 NatSCEV; 4112 (34.6%) in the 2011 NatSCEV; and 3738 (31.4%) in the 2014 NatSCEV; 5532 (46.5%) were aged 2 to 9 years (2785 [50.4%] aged 2-5 years; 2693 [48.7%] girls; 3521 [63.7%] White children), and 6365 (53.5%) were aged 10 to 17 years (3612 [56.7%] aged 14-17 years; 3117 [49.0%] female participants; 4297 [67.5%] White individuals). Among participants aged 2 to 9 years, no clinical contact was reported for 57% (95% CI, 51%-62%) of the high ACE group, 53% (95% CI, 48%-58%) of the high distress symptom group, and 41% (95% CI, 32%-51%) of the group with high levels on both indicators. Among participants aged 10 to 17 years, the group with no clinical contact comprised 63% (95% CI, 56%-69%) of the high ACE group, 52% (95% CI, 46%-57%) of the high distress symptom group, and 62% (95% CI, 51%-71%) of youth scoring high on both indicators. Among racial groups, odds of contact were very low for Black children aged 2 to 9 years with high ACEs compared with non-Hispanic White children with the same age and exposure (odds ratio, 0.26; 95% CI, 0.14-0.49). In this cross-sectional study combining findings from 3 US national surveys, large portions of children at high risk because of adversity or mental health symptoms were not receiving clinical services. Better ways are needed to find these at-risk populations and help them obtain relevant intervention resources.