Study 1: TCCS (North Tyrol vs. South Tyrol)Study design and sample

The TCCS, which was implemented in North Tyrol (Austria) and South Tyrol (Italy), aimed to investigate the impact of the COVID-19 pandemic on 3–13-year-olds, taking the perspective of children, parents, and educators into account, and was performed online using the CHES software (Evaluation Software Development, Innsbruck, Austria) between March 2020 and July 2022. Parents were recruited from schools and advertisements in local media. The eligibility criteria were living in North Tyrol or South Tyrol, children aged 3–13 years, proficiency in the German language, and the cognitive ability to fill out an online questionnaire.

For comparison with COP‑S 2021, we present child- and parent-reported responses for schoolchildren aged between 7 and 13 years at the third timepoint (June to July 2021). In this substudy, the children completed 141 online questionnaires (North Tyrol, 101; South Tyrol, 40), and the parents 402 (North Tyrol, 291; South Tyrol, 111).

The study was approved by the Ethics Committees of the Medical University of Innsbruck (no.1183/2020), and written consent was obtained from the participants’ families. The ethical vote of the Medical University of Innsbruck also applies to the German-speaking population of South Tyrol.

Measures Child and Adolescent Trauma Screening (CATS 7–17)

Children and their parents completed the German version of the CATS for children and adolescents [16]. It gathers information about a child’s behavior, emotions, and experiences related to trauma during the last 2 weeks on a four-point symptom response scale from 0 “never,” 1 “once in a while,” 2 “half the time,” to 3 “almost always.” The CATS assesses various domains, including re-experiencing, avoidance, negative mood, and cognition, as well as arousal symptoms. The cut-off ≥ 21 of the total trauma symptom score was used as an indication of a clinically relevant level of symptoms.

Children Anxiety Test (KAT-III)

Perceived anxiety and trait anxiety from children’s perspectives were assessed using the German KAT-III [17]. This helps identify children who may experience elevated levels of anxiety. This test can be valuable in diagnosing anxiety disorders, tracking changes in anxiety symptoms over time, and evaluating the effectiveness of interventions aimed at reducing anxiety in children. The 18 items are rated using yes/no responses.

Child Behavior Checklist (CBCL)

Parents completed the German version of the CBCL for children aged 6–18 years [18]. The CBCL is designed to assess a wide range of behavioral and emotional problems in children and adolescents. The items are rated on a three-point Likert scale (0 = “absent,” 1 = “occurs sometimes,” 2 = “occurs often”). Raw scores for each scale are converted to norm-referenced T‑scores (mean [M] = 50, standard deviation [SD] = 10), with separate norms provided for each gender within the 6–11 and 12–18-year age ranges. “Clinically significant” elevations are indicated by T‑scores ≥ 64 on the broadband scales, and ≥ 70 on the syndrome scales. “Borderline” elevations range from 60–63 and 65–69 on the broadband and syndrome scales, respectively. In this study, parents were specifically asked to assess their children’s behavior in relation to internalizing problems and aggressive behavior using the CBCL. The internalizing problems scale includes items related to emotionally reactive behaviors, anxiety/depression, somatic complaints, withdrawal behavior, and sleep problems.

Posttraumatic growth (PTG)

PTG, defined as positive changes resulting from an individual’s struggle with traumatic or stressful events [19], was measured using the open-ended question: “What positive changes occurred for your child due to the COVID-19 crisis?” To understand the phenomenon of posttraumatic change more comprehensively, the construct was expanded to include possible negative experiences [20]. In the second open-ended question, parents were asked, “What negative changes occurred for your child due to the COVID-19 crisis?” If parents’ responses indicated one or more positive impact, PTG was scored as 1 (“yes”); if parents stated that they did not notice any positive impact, PTG was scored as 0 (“no”). The qualitative results were only quantified for “positive changes.”

Data analysis

Child- and parent-reported responses were compared between North and South Tyrol. For continuous variables following normal distribution, we used t-tests for two-group comparisons. For non-normally distributed data, Wilcoxon rank sum tests, M, and SD were used to describe continuous variables. For ordinal data, Pearson’s chi-square test and Fisher’s exact test for count data were used to compare frequencies (counts), and statistical analyses were performed using the statistical software package R Studio (MA, USA) version 2022.07.2.

The written answers of the parents (qualitative data) were analyzed with MAXQDA 2022 software (VERBI – Software, Berlin, Germany) for qualitative data. In collaboration with the second author, the last author conducted the qualitative data analysis applying the thematic analysis qualitative research method (TA; [21]). We approached TA in an inductive way, i.e., codes and themes were developed directly from the data. Our aim was to understand the possible positive and negative effects of the corona crisis on children from a parents’ perspective at this specific measurement point. With the crosstab function of MAXQDA, we compared the North Tyrolian sample with the South Tyrolian sample based on variable values.

Study 2: COP-S 2021 study (South Tyrol)Study design and sample

The questionnaire used in COP‑S 2021 was the COPSY Germany 2020 questionnaire [22]. The study design and methodology were similar to those of the Germany-wide, longitudinal, representative BELLA study [23], which is the module for examination of the mental health of children and adolescents.

The province-wide, population-based COP‑S 2021 was conducted as an anonymous online survey. In collaboration with the public schools’ administration, 38,400 families with children attending a public school were invited by email to participate. The online survey used the SoSci Survey Software, version 3.2.46 (SoSci Survey GmbH, Munich, Germany). After 1 week, the invitation was repeated. From May 28, 2021, to June 16, 2021, when schools started to open again after the lockdown, 6952 parents of children and adolescents aged 7–19 years participated in the online study. A total of 5159 questionnaires were completed. In addition, 2163 self-reports were gathered from children aged 11–19 years [12]. Of these completed and analyzed questionnaires, 3402 were from parents of children aged 7–13 years, and 939 were self-reports from children aged 11–13 years.

The study was approved by the Ethics Committees of South Tyrol (code 52-2021 on April 21, 2021). Parents consented to participate at the beginning of the online questionnaire.

Measures

Adolescents aged 11 to 13 years responded to the self-report version of the online survey, and parents of children aged 7–13 years answered the parent proxy version. The parent proxy survey included questions on the age and gender of children and adults, marital status, migration background, single parenthood, and parental education (CASMIN index [24, 25]).

Screen of Child Anxiety Disorders (SCARED)

The SCARED [25,26,27,28] is a questionnaire that contains nine items assessing recent symptoms of generalized anxiety disorder (GAD). In this study, adolescents completed the child version of the SCARED and were asked the frequency of each symptom on a three-point-scale: 0 (almost never), 1 (sometimes), 2 (often). A total score of 25 or above has been suggested to indicate the presence of clinically significant anxiety.

Health Behaviour in School-Aged Children (HBSC)

The HBSC [29] is a questionnaire used to assess various psychosomatic problems experienced by young people. Both parents and adolescents were asked to report the frequency of the eight symptoms that had occurred in the past week. The adolescents responded to these questions by choosing one of the following five answer categories: “rarely or never,” “about every month,” “about every week,” “more than once a week,” and “about every day.” Prevalences were calculated for all symptoms occurring at least about every month.

Support during the COVID-19 pandemic and qualitative data (open-ended questions)

Parents were asked where they had wished to receive support during the last months using five categories they could choose from: “dealing with school problems of my child,” “dealing with the feelings of my child,” “dealing with my child’s behavior,” “returning to normality after the lockdown for my child,” and “dealing with relations within our family.”

Furthermore, it was possible to add answers in an open field regarding other support the parents would have wished for which was not already mentioned as a category in the questionnaire.

Data analysis

The data were analyzed using descriptive statistics, using M and SD for metric variables, and absolute and relative frequencies for nominally and ordinally scaled variables. Chi-square tests were performed to compare categorical variables. Parents’ and children’s responses were compared using McNemar’s test. Significance levels of alpha < 0.05, < 0.01, and < 0.001 are reported. All statistical analyses were performed using SPSS version 25.0.0 (IBM Corp., Armonk, NY, USA).