An estimated 10–20% of children worldwide experience some form of mental health difficulties [54], such as ADHD and internalizing symptomology. To provide insight into preschoolers’ ADHD and internalizing behaviors, this study employed a longitudinal design and investigated the influence of putative risk factors from birth and age 4 and behavioral outcomes assessed at age 5. Our study highlights the importance of considering child behaviors and household environmental factors, and most importantly their interaction, in predicting problem behaviors. A unique contribution of our study was consideration of these same risk factors as predictors of 5-year-old ADHD as well as internalizing behaviors. Overall, we found that children with low effortful control who also showed high activity levels during testing were significantly more likely to be rated higher on ADHD. However, for children from homes
characterized by low household chaos, having high temperamental activity appeared to provide a protective effect, as it predicted lower 5-year-old internalizing. Thus, early childhood activity levels could be protective or a risk factor, depending on either temperament or the household environment and depending on the behavior outcome under consideration.
This study had three aims: 1) to examine whether perinatal stress, child temperament and general activity level, and household chaos, as well as their interactions, contributed to preschoolers’ ADHD behaviors; 2) to determine whether these same risk factors predicted 5-year-old internalizing behaviors. With respect to the first aim, our results indicated a significant effect of high child temperamental activity at age 4 predicting higher ADHD behaviors one year later. Additionally, a significant interaction between age 4 observed activity and 4-year-old temperamental effortful control indicated that, for children with low effortful control, high observed activity predicted higher parent-reported ADHD behaviors at age 5.
Earlier studies exploring temperament qualities as potential risk factors for ADHD have found that children who are inattentive and have difficulty delaying responses at age 2 exhibit hyperactivity, inattention, and aggression at age 4 [55]. Children with behavioral disinhibition are significantly more likely than non-disinhibited children to have ADHD and comorbid mood and disruptive behavior disorders [56]. Recent research examining factors linking early temperament and later ADHD showed that negative emotionality during preschool is positively associated with ADHD symptom severity in middle childhood, but developing executive control mediates this relation [35]. Similarly, our study showed that children with greater effortful control were protected from parent-reported ADHD behaviors even if they showed higher levels of activity during testing. Indeed, poorer (low) effortful control has been shown to be a risk factor for later externalizing [57]. However, framed within the context of our findings, this may be true specifically for children with high activity levels. Future research should focus on identifying additional variables that play a role in the pathway between temperament and ADHD symptom severity, with a focus on further elucidating the mechanisms by which temperament exerts its harmful effects in order to help inform additional treatment options.
With respect to our second aim, we found that higher household chaos predicted greater parent-reported internalizing behaviors at age 5, underscoring the risk that chaotic homes may pose for later anxious, depressed, and withdrawn behaviors. Interestingly, a significant 4-year-old temperamental activity by household chaos interaction demonstrated that although elevated chaos at home was generally associated with higher internalizing, children with low activity levels even in low chaos homes also showed high internalizing symptoms. However, in low chaos households, children with high age 4 temperamental activity had significantly lower parent-reported internalizing at age 5.
Preschoolers in high-conflict homes are more likely to experience significant anxiety than preschoolers in low-conflict homes [58]. Among the few empirical studies that have incorporated different aspects of household chaos and early childhood behavior problems, Wilhoit and colleagues (2021) reported that greater household chaos was associated with more internalizing and externalizing behavior problems, but the association was no longer reported in homes with good, responsive mother-child relationships. Their study found that the effects of chaos depended on mother-child relations, and our study found that the effects of chaos were mitigated by children's activity levels. Clearly it is important to examine the home environment, as individual differences in children lead to differences in behavioral outcome depending on chaotic home environments.
Internalizing disorders in early childhood have been under-studied in comparison to externalizing disorders, in part because reporters are less aware of internalizing problems in children [59]. However, internalizing symptoms are relatively common in young children and their trajectory has remained relatively stable [60]. Internalizing disorders are associated with negative family environments, poor child temperament, problematic peer relationships, and stressful life events [36]. There is also a relationship between family structure and preschool internalizing problem behaviors like anxiety; children with more siblings in their households and those who do not live with both biological parents are more likely to develop preschool problem behaviors [61]. Therefore, given their high prevalence rates and the strong likelihood that these disorders will persist throughout development, it is crucial to evaluate, intervene, and recommend treatments for internalizing behaviors in young children.
Most interesting were the findings indicating that ADHD and internalizing behaviors at age 5 varied depending on individual characteristics (child temperament and general activity levels) and contextual factors (household chaos). Specifically, the greater risk for ADHD behaviors posed by elevated observed activity levels (i.e., state-level) was mitigated by 4-year-old effortful control, whereas high age 4 temperamental activity (i.e., trait-level) appeared to lessen the risk posed by household chaos for later internalizing behaviors. Taken together, these results highlight the importance of both child- and family-level characteristics when assessing risk for later behavioral problems. Early childhood temperament is one of the few behavioral characteristics that predict clinically significant outcomes beyond childhood, and sometimes even into adulthood [62, 63].
With respect to environmental factors, change in household income, home environment, and parental rearing style are associated with ADHD [64, 65]. In addition, the role of certain gestation-related risk factors in the pathogenesis of ADHD has attracted attention (e.g., maternal stress, anxiety, depression, and sleep disturbances during pregnancy) [30]. Such associations pertaining to the perinatal environment are also of particular concern, as birth complications during this period are associated with a greater risk of brain injury during assisted modes of delivery [66]. In this way, it was surprising that we found no relationship between birth complications and either ADHD or internalizing. It is possible that specific complications (e.g., birth asphyxia, preeclampsia) need to be examined, as opposed to employing a global measure as was done in the current study.
Clinical Implications
Researchers often observe inadequate parenting, poor emotional environment, and household chaos in families of children with ADHD. These factors can be a predictor for many other behavior problems in children. Clinicians should develop recommendations aimed at parent training intended to help parents establish fixed routines and rituals and organize daily life more efficiently. One relatively quick and easy option for clinicians would be to ask parents to complete the Confusion, Hubbub, and Order Scale (CHAOS [42]), as we found it a significant predictor of later internalizing problem behaviors for preschoolers. They might also consider utilizing a short temperament survey, which would provide them with important information for later potential behavior problems. One option includes the Integrative Child Temperament Screener (ICTS [67]), a new nine-item scale that shows good validity when compared to the CBCL [68].
Strengths And Limitations
This study is strengthened by our employing a multi-method approach and using a longitudinal design. For example, both child temperamental activity levels (trait-level activity) and general activity levels observed in the laboratory (state-level activity) were assessed; both measures predicted 5-year-old ADHD behaviors. Another example includes our parent-rated measure of birth complications, which has been shown to be both valid and reliable [47]. Finally, collecting information on the putative risk factors in early childhood affords insight into certain characteristics that may precede the emergence of preschoolers’ ADHD and internalizing behaviors, information that could be used to help discern children who may be at greater risk for these problem behaviors.
This study also has several limitations that must be considered. First, our sample size was relatively small, making it difficult to detect small effects, although we certainly were able to detect moderate and large effects, which are the most clinically significant. Another limitation includes our use of parent-reported measures at age 5, especially for internalizing behaviors, as parent-report bias (over-/under-rating) might be an issue. Potentially, these ratings may not accurately reflect what the child would report experiencing [59]. However, for very young children, like preschoolers, given developing cognitive abilities, a parent-report measure likely provides more accurate assessments than a child could provide on their own [69]. Third, our study utilized a non-clinical sample of typically-developing children and, therefore, may not entirely capture the etiology of clinical-level ADHD and internalizing symptomology. Future research should investigate the role of child temperament and household characteristics for the development of later problem behaviors using children from clinical samples. Finally, our sample was comprised of twins. There is a possibility that parents of twins expect birth complications, and therefore the complications may not predict later problem behaviors if parents’ expectations differed from parents of singletons and if those expectations affect either child behavior or parental interpretations of behaviors.
Future Directions
Future research should focus on the protective factors that shield young children from these behavior problems, leading to more effective and targeted treatments. Identifying additional variables that play a role in the onset of ADHD and internalizing in children and understanding the mechanisms by which these risk factors exert their harmful effects will be a challenge for future researchers. It is crucial to evaluate and recommend treatments for both ADHD and internalizing disorders in children, given their high prevalence rates and their risk of persisting throughout a child's life.
Summary
Trends indicate rising rates of ADHD and internalizing behaviors in children, which underscore the need for continued investigation into the etiology of these disorders. Overall, our results demonstrate that individual- and family-level factors, including child activity and effortful control as well as household chaos, independently and interactively predict ADHD and internalizing behaviors in preschool-age children. The importance of considering child temperament and household environment in a clinical setting to better assess preschool children is recommended.