Meeting 24-h movement behaviors (24-HMB: physical activity [PA], screen time [ST], and sleep [SL]) recommendations may be associated with positive health outcomes among youth with specific mental, behavioral, and neurodevelopmental (MBD) conditions. However, temporal trends and disparities in meeting 24-HMB guidelines in these higher-risk groups have not been investigated, hampering the development of evidence-based clinical and public health interventions. Serial, cross-sectional analyses of nationally National Survey of Children's Health (NSCH) data (including U.S. youth aged 6-17 years with MBD conditions) were conducted. The time-trends survey data was conducted between 2016 and 2021. The prevalence of 24-HMB adherence estimates were reported for the overall sample and for various sociodemographic subgroups. The subgroups analyzed included: age group (children[aged 6 to 13 years], adolescents[aged 14 to 17 years]), sex, socioeconomic status, and ethnicity. Data on 52,634 individuals (mean age, 12.0 years [SD,3.5]; 28,829 [58.0 %] boys) were analyzed. From 2016 to 2021 the estimated trend in meeting PA + ST + SL guidelines declined (-0.8 % [95%CI, -1.0 % to -0.5 %], P for trend <0.001), whereas meeting none of 24-HMB guidelines increased (2.2 % [1.8 % to 2.6 %], P for trend <0.001). White participants, children, and boys reported higher estimated prevalence of meeting full integrated (PA + ST + SL) guidelines. The temporal trends observed in this study highlight the importance of consistently monitoring movement behavior among MBD youth and identifying variations by sociodemographic groups in meeting 24-HMB guidelines for health promotion within these vulnerable groups.