It is a common belief that new generations of children are in decline (Protzko & Schooler, 2019). However, contrary to the belief that new generations decline, children’s ability to delay gratification, measured by the famous ‘Marshmallow Test’, for example, has actually improved from the 1960s to the 2010s (Protzko, 2020). This means that (at least when it comes to food) young children today can resist rewards for a longer time than they did 50 years ago. This might be mainly due to an improvement in the living standards of families, an increase in parental educational level, the number of years children spend in education, and improvements in nutrition and healthcare services (Protzko, 2020). This increase in delay of gratification ability is similar to the ’Flynn effect’ which refers to the sustained increase in intelligence and cognitive domains worldwide during the 20th century (Pietschnig & Gittler, 2015). However, since the 2000s, stagnation or even reversal in intelligence (Dutton et al., 2016), attention, and working memory (Graves et al., 2021; Wongupparaj et al., 2017) have been observed in many countries worldwide, named as the ’negative Flynn effect’. 

Along with the ’negative Flynn effect’, there have been other problematic trends reported among young adults, for example, self-reported loneliness has been increasing (Buecker et al., 2021), and emotional intelligence-related traits like well-being, self-control, and emotionality have been decreasing (Khan et al., 2021), with a similar negative trend in resilience (Zhao et al., 2022). These changes over the last decades have been proposed to be caused by complex twofold changes on the level of individuals and their environment (Buecker et al., 2021; Graves et al., 2021; Khan et al., 2021; Zhao et al., 2022). According to the mutual constitution model (Markus & Kitayama, 2010), the socio-cultural environment of different time periods is likely to shape the individual with its problems and vice-versa. 

Importantly, these negative trends affecting the mental health of youth can be reversed with targeted interventions or prevention programs in education and/or healthcare. Yet, there is a lack of comprehensive research about time trend changes in childhood and adolescence regarding emotional and behavioral problems. Consequently, the aim of the present meta-analysis was to explore cross-temporal changes in the emotional and behavioral functioning of European children and adolescents and reveal if there are any specific problems that are on the rise and require immediate attention.

Studies that used the famous cross-culturally validated Child Behavior Checklist (CBCL) by Achenbach and Edelbrock (1983), or Achenbach’s Teacher-Reported Form (TRF), or the Youth Self-Reported (YSR) version of the checklist with population-based representative samples of 1-18 years old children were systematically searched in four databases (i.e., Web of Science, Scopus, Google Scholar, PubMed). For inclusion in this cross-temporal meta-analysis, studies had to report the raw means and standard deviations of the CBCL, TRF, or YSR. As the checklist has changed it’s possible maximum points in 2001, the percentage of possible maximum points (POMP) were calculated from the raw means and standard deviation (Buecker et al., 2021). The inclusion criteria were set for only European population-based samples of youth for this analysis. The systematic search and selection procedure was performed by the main author and trained research assistants. There were more than 4000 studies screened by their title and abstract, and after the full-text selection only 58 remained for this analysis.

For the identification of any non-linear changes due to children’s age, three age groups were set: early childhood (1-6 years), middle childhood (7-14 years), and teens (14-18 years). Mixed-gender meta-regressions showed a significant increase in somatic complaints, such as headache or stomachache without a medical cause, in early childhood (k = 5, b year = 0.385, p = .03) and middle childhood (k = 5, b year = 0.216, p = .05) over the last decades according to parents opinion, and a marginally significant increase in adolescence as well (k = 6, b year = 0.209, p = .06). Parents also reported a large increase in 1-6 years old children’s externalizing problems, more specifically aggression and attention problems, over the last 20 years (k = 10, b year = 0.626, p = .04). Among 7-14 years old children the same externalizing problem subscale, but for this age group it involves aggression and deviant behavior, showed a significant decrease (k = 22, b year = -0.375, p = .05) as reported by parents. The meta-regression analysis of teenage samples showed a significant increase in anxious-depressed problems over the last decades according to parent reports (k = 7, b year = 0.310, p = .02), but a decrease in aggression according to youth’s self-report (k = 7, b year = -0.601, p = .03). When girls and boys were analyzed separately, mete-regression revealed an increase in 7-14 years old European boys’ attention problems (k = 10, b year = 1.087, p = .01), and a somewhat smaller increase in European girl’s attention problems (k = 10, b year = 0.884, p = .02). Gender-specific differences were found in the change of social problems in middle childhood: girls showed a significant increase in social problems over time (k = 9, b year = 0.620, p = .05), while the increase in such problems among boys was non-significant (k = 9, b year = 0.498, p = .09).

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