QuestionMental disorders typically start in childhood and persist, causing high individual and collective burdens. To inform policymaking to address children’s mental health in high-income countries we aimed to identify updated data on disorder prevalence.MethodsWe identified epidemiological studies reporting mental disorder prevalence in representative samples of children aged 18 years or younger—including a range of disorders and ages and assessing impairment (searching January 1990 through February 2021). We extracted associated service-use data where studies assessed this. We conducted meta-analyses using a random effects logistic model (using R metafor package).FindingsFourteen studies in 11 countries met inclusion criteria, published from 2003 to 2020 with a pooled sample of 61 545 children aged 4–18 years, including eight reporting service use. (All data were collected pre-COVID-19.) Overall prevalence of any childhood mental disorder was 12.7% (95% CI 10.1% to 15.9%; I2=99.1%). Significant heterogeneity pertained to diagnostic measurement and study location. Anxiety (5.2%), attention-deficit/hyperactivity (3.7%), oppositional defiant (3.3%), substance use (2.3%), conduct (1.3%) and depressive (1.3%) disorders were the most common. Among children with mental disorders, only 44.2% (95% CI 37.6% to 50.9%) received any services for these conditions.ConclusionsAn estimated one in eight children have mental disorders at any given time, causing symptoms and impairment, therefore requiring treatment. Yet even in high-income countries, most children with mental disorders are not receiving services for these conditions. We discuss the implications, particularly the need to substantially increase public investments in effective interventions. We also discuss the policy urgency, given the emerging increases in childhood mental health problems since the onset of the COVID-19 pandemic (PROSPERO CRD42020157262).

QuestionOppositional defiant and conduct disorders (ODD and CD) start early and persist, incurring high individual and collective costs. To inform policy and practice, we therefore asked: What is the best available research evidence on preventing and treating these disorders?Study selection and analysisWe sought randomised controlled trials (RCTs) evaluating interventions addressing the prevention or treatment of behaviour problems in individuals aged 18 years or younger. Our criteria were tailored to identify higher-quality RCTs that were also relevant to policy and practice. We searched the CINAHL, ERIC, MEDLINE, PsycINFO and Web of Science databases, updating our initial searches in May 2017. Thirty-seven RCTs met inclusion criteria—evaluating 15 prevention programmes, 8 psychosocial treatments and 5 medications. We then conducted narrative synthesis.FindingsFor prevention, 3 notable programmes reduced behavioural diagnoses: Classroom-Centered Intervention; Good Behavior Game; and Fast Track. Five other programmes reduced serious behaviour symptoms such as criminal activity. Prevention benefits were long term, up to 35 years. For psychosocial treatment, Incredible Years reduced behavioural diagnoses. Three other interventions reduced criminal activity. Psychosocial treatment benefits lasted from 1 to 8 years. While 4 medications reduced post-test symptoms, all caused important adverse events.ConclusionsConsiderable RCT evidence favours prevention.Clinical implicationsEffective prevention programmes should therefore be made widely available. Effective psychosocial treatments should also be provided for all children with ODD/CD. But medications should be a last resort given associated adverse events and given only short-term evidence of benefits. Policymakers and practitioners can help children and populations by acting on these findings.

QuestionAnxiety disorders are the most prevalent childhood mental disorders. They also start early and persist, causing high individual and collective costs. To inform policy and practice, we therefore asked: What is the best available research evidence on preventing and treating these disorders?MethodsWe sought randomised controlled trials (RCTs) evaluating interventions addressing anxiety problems in young people. We identified RCTs by searching CINAHL, ERIC, MEDLINE, PsycINFO and Web of Science. Thirty-three RCTs met inclusion criteria—evaluating 8 prevention programmes, 12 psychosocial treatments and 7 pharmacological treatments. We then conducted meta-analyses by intervention type.FindingsFor prevention, the cognitive-behavioural therapy (CBT) programme Coping and Promoting Strength stood out for reducing anxiety diagnoses. For psychosocial treatment, 9 CBT interventions also reduced diagnoses: Cool Kids; Cool Little Kids Plus Social Skills; Coping Cat; Coping Koala; One-Session Treatment; Parent Education Program; Skills for Academic and Social Success; Strongest Families and Timid to Tiger. Successful CBT interventions were used with children ranging from pre-schoolers to teens in homes, communities/schools and clinics. For pharmacological treatment, selective-serotonergic-reuptake-inhibitors (SSRIs) significantly improved symptoms. Fluoxetine stood out for also reducing post-test diagnoses, but caused adverse events. Meta-analyses indicated strongest effects for CBT (Log OR=0.95; 95% CI, 0.69 to 1.21) and SSRI treatments (1.57; 1.09 to 2.06).ConclusionsCBT is effective for preventing and treating childhood anxiety—across a range of ages and formats. Fluoxetine is also an effective treatment but side effects must be managed. CBT prevention and treatment interventions should be made widely available, adding fluoxetine in severe cases.