Early childhood internalizing problems, externalizing problems and their co-occurrence and (mal)adaptive functioning in emerging adulthood: a 16-year follow-up study

PURPOSE: A vast amount of studies suggest that internalizing or externalizing problems are related to individual functioning, and often co-occur. Yet, a focus on their additive and interactive effects is scarce. Furthermore, most research has focused on a limited number of developmental domains and mostly on maladaptive functioning. Therefore, the current prospective study examined whether early childhood (ages 4–8) internalizing and externalizing problems and their interaction were related to a broad range of (mal)adaptive functioning outcomes in emerging adulthood (ages 20–24). METHODS: Data from the Flemish Study on Parenting, Personality and Development were used. At Time 1 (1999) mothers of 374 children (45% boys) and fathers of 357 children (46% boys) rated internalizing and externalizing problems through the Child Behavior Checklist. Outcomes in emerging adulthood were measured through self-reports 16 years later across the following domains: psychological functioning, social functioning, work, physical health, and self-concept. RESULTS: Early externalizing problems were related to maladaptive outcomes on the psychological and social domains. With regard to adaptive functioning, externalizing problems were associated with lower satisfaction regarding general health on the physical domain. Early internalizing problems were not associated with any emerging adulthood outcomes. The interaction of (father reported) internalizing and externalizing problems was related to aggressive behavior. CONCLUSION: Early childhood externalizing problems were associated with maladaptive and adaptive functioning over a time span of 16 years. The results add to studies on the implementation of prevention and intervention programs in early childhood and to the value for developing personalized interventions. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00127-020-01959-w) contains supplementary material, which is available to authorized users.