From 2020 to 2023, the coronavirus-19 (COVID-19) pandemic exposed children to a variety of adverse childhood events, including parental loss, abuse, and disruption in services, and it exacerbated societal inequities. Studies evaluating the mental health of older children and adolescents reported increases in depression and anxiety symptoms, but no reviews have addressed the effects of the pandemic on preschool children. This systematic review and meta-analysis is the first to explore these effects. The goal was to analyze and synthesize longitudinal cohort studies to determine impact of the COVID-19 pandemic on the development and mental health of young children. Searches of multiple databases were performed for studies published between 2018 and 2023 with pre- and post-pandemic evaluations of the mental health or development of preschool children (aged 0–6 years) using objective measures and according to Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Cohen’s d effect sizes were calculated for each study that utilized the Strengths and Difficulties Questionnaire (SDQ), Ages and Stages Questionnaire (ASQ), or the Child Behavior Checklist (CBCL). Random-effects mixed models combined the estimates of effect sizes to calculate the overall mean effect size. The meta-analyses included 22,348 children from 16 countries. The analyses showed small increases in emotional symptoms and conduct problems, as well as increases in emotional reactivity, anxiety/depression, withdrawal symptoms, attention problems, and aggressive behaviors. A decrease in fine motor and personal–social skills was noted. Studies not included in these meta-analyses also showed negative effects on language and executive function. This systematic review characterizes the detrimental effects of the COVID-19 pandemic on the mental health and development of preschool children across the world. Our results suggest the vulnerability of early childhood to pandemic-related disruptions, although the heterogeneity in study design and child characteristics may limit some of these conclusions.

Background: We report the prevalence of children with multiple medical symptoms in a pediatric neurology clinic, describe their symptom profiles, and explore their association with adverse childhood experiences (ACEs). Methods: We retrospectively reviewed 100 consecutive patients from an outpatient pediatric neurology clinic. Patients were included if they were ≥5 years old and reported ≥4 symptoms that were unexplained for ≥3-months. Symptom profiles across six functional domains were recorded: (1) executive dysfunction, (2) sleep disturbances, (3) autonomic dysregulation, (4) somatization, (5) digestive symptoms, and (6) emotional dysregulation. ACEs were scored for all patients. Results: Seventeen patients reported ≥4 medical symptoms. Somatization, sleep disturbances, and emotional dysregulation occurred in 100% patients, with executive dysfunction (94%), autonomic dysregulation (76%), and digestive problems (71%) in the majority. Forty-two children reported ≥1 ACE, but children with ≥4 symptoms were more likely to report ACEs compared to other children (88% vs. 33%; p < 0.0001) and had a higher median total ACE score (3 vs. 1; p < 0.001). Conclusions: Children with multiple medical symptoms should be screened for potential exposure to ACEs. A clinical profile of symptoms across multiple functional domains suggests putative neurobiological mechanisms involving stress and nervous system dysregulation that require further study.

Positive childhood experiences (PCEs) are increasingly recognized as critical factors that promote resilience, emotional regulation, and flourishing in children, especially in the context of adversity. This narrative review explores the conceptual development, empirical evidence, and theoretical frameworks underpinning the role of PCEs in early childhood development. A critical assessment of the existing literature focuses on how PCEs function as promotive and protective factors and evaluates the strengths and limitations of current measurement tools. Drawing on theories from resilience science, developmental psychopathology, positive psychology, and ecological systems theory, this review highlights the complex, multidimensional nature of PCEs and their interplay with parenting styles, socioeconomic status, and the social drivers of health. Despite compelling evidence that PCEs influence cognitive, emotional, relational, and behavioral outcomes across the lifespan, there is no dedicated validated tool for prospectively measuring PCEs in preverbal or preschool-aged children. This gap limits our ability to design and test interventions to mitigate adverse childhood experiences and to assess their developmental impact in real time and subsequent periods. We conclude that future research should focus on creating culturally sensitive, developmentally appropriate instruments to measure PCEs in early life, essential for advancing equity, optimizing child health, and promoting wellness across diverse populations.

The SKY Schools Program combines breath-based techniques and a social-emotional learning curriculum. We examined its effects on objective physiological biomarkers, including hair cortisol (HCC, chronic stress measure) and hair oxytocin (HOC, social affiliation measure), as well as behavioral (youth risk behaviors) and mental health outcomes (anxiety, depression). The SKY Schools program was adapted for post-pandemic restrictions (i.e., staff shortages, no lessons requiring writing, limited weekly follow-ups) and implemented among 7th grade students (daily in-person 40-min sessions for three weeks during physical education classes). Longitudinal assessments were obtained at baseline (T1, February 2022, N = 21), post-intervention (T2, June 2022, N = 20), and follow-up (T3, December 2022, N = 18). Most of our sample was male (67 %), Hispanic (62 %), and lived in low-income (<$100K) households (75 %). Students reported fewer poor mental health days at follow-up (Friedman test p < 0.01). Log-normal (Ln)-HCC (p < 0.01) were higher post-intervention vs. baseline (median 1.81 (IQR 1.63–2.46) vs. 1.60 (0.91–1.85)) and lower at follow-up (1.23; IQR: 0.64–1.50), with HCC in more students moving into the adaptive range (25th-75th percentile). Ln-HOC (p = 0.04) were higher post-intervention vs. baseline (1.78 (1.54–2.26) vs. 1.50 (0.81–1.70)). This study uniquely evaluated the impact of the SKY intervention on hair cortisol (HCC) and hair oxytocin concentrations (HOC), which are objective, physiological measures of chronic stress and social affiliation. Results suggest that SKY may improve social affiliation and possibly HPA-axis regulation.

Background. Early childhood experiences have long-lasting effects on subsequent mental and physical health, education, and employment. The measurement of these effects relies on insensitive behavioral signs, subjective assessments by adult observers, neuroimaging or neurophysiological studies, or retrospective epidemiologic outcomes. Despite intensive research, the underlying mechanisms of these long-term changes in development and health status remain unknown. Methods. We analyzed scalp hair from healthy children and their mothers using an unbiased proteomics platform combining tandem mass spectrometry, ultra-performance liquid chromatography, and collision-induced dissociation to reveal commonly observed hair proteins with a spectral count of 3 or higher. Results. We observed 1368 non-structural hair proteins in children and 1438 non-structural hair proteins in mothers, with 1288 proteins showing individual variability. Mothers showed higher numbers of peptide spectral matches and hair proteins compared to children, with important age-related differences between mothers and children. Age-related differences were also observed in children, with differential protein expression patterns between younger (2 years and below) and older children (3–5 years). We observed greater similarity in hair protein patterns between mothers and their biological children compared with mothers and unrelated children. The top 5% of proteins driving population variability represented biological pathways associated with brain development, immune signaling, and stress response regulation. Conclusions. Non-structural proteins observed in scalp hair include promising biomarkers to investigate the long-term developmental changes and health status associated with early childhood experiences.

Background: Adverse childhood experiences (ACEs) can lead to hypothalamic–pituitary–adrenal axis dysregulation, negatively impacting child growth and development. Methods: The Hair Biomarkers Study (HBS-I) evaluated healthy preschool children using parent-reported surveys, anthropometrics, and painlessly obtained scalp hair to measure hair cortisol (HCC; ng/mg) and oxytocin concentrations (HOC; ng/mg) via ELISA; log-transformed data were used in analyses. Height, weight, and BMI percentiles were based on CDC growth curves. Linear regressions examined associations of child and maternal hair biomarkers with percentiles, adjusting for sociodemographic factors. Results: The median age was 39.1 months (IQR 23.5–53.0, N = 1189). Higher child Ln-HCC was associated with an increased BMI percentile (0.027; 95%Cl: 0.013, 0.040), while higher child Ln-HOC was associated with a decreased BMI (−0.016; 95%Cl: −0.028, −0.005). Similar significant associations were observed between maternal biomarkers and child growth. In models mutually adjusted for mother and child hair biomarkers, maternal Ln-HCC was associated with an increased BMI percentile (0.036; 95%Cl: 0.003, 0.069), while maternal Ln-HOC was associated with a decreased BMI percentile (−0.034; 95%Cl: −0.052, −0.016). Maternal ACEs of 2–3 vs. 0–1 were associated with increased child weight (0.057; 95%Cl: 0.003, 0.112) and BMI percentiles (0.076; 95%Cl: 0.017, 0.135). Conclusions: We show that higher maternal and child HCC was associated with increased child BMI percentiles, while higher HOC was linked with decreased BMI percentiles. Hair biomarkers may reflect the effects of nurturing vs. adverse experiences during critical windows of growth and development in early childhood.