Change in level of aggressive behaviour in children: Child Behavior Checklist (CBCL) 11/2-5 and 6-18, parent-report, sub-scale "Aggressive behaviour" (with 19 items (CBCL ½ - 5) and 18 items (CBCL 6-18), continuous sub-scale score

The primary outcome child oppositional aggressive behaviour is assessed with 3 indicators: 1) parent-report: The CBCL is part of the Achenbach System of Empirically Based Assessment (ASEBA) and is available for different age ranges, including the targeted range in the present study. For Phase 3, the parent-report versions for children aged 1½-5 and 6-18 are employed. The aggressive behaviour sub scale (CBCL ½ - 5 version: 19 items, CBCL 6-18: 18 items) belongs to the externalising scale and assesses aggressive behaviour (e.g., "Argues a lot"). The total raw score ranges from 0 to 38 in the CBCL ½ - 5 version and 0-36 in the CBCL 6-18 version, with higher scores indicating more aggressive child behaviour. Items are rated on a 3-point Likert scale (2 = very true or often true of the child; 0 = not true of the child).

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in prevalence of Externalising Disorders in Children (MINI-KID), binary total score

The primary outcome child oppositional aggressive behaviour is assessed with 3 indicators: 2) clinical interview: The Mini International Neuropsychiatric Interview for Children and Adolescents - Parent Version (MINI-KID-P) will be used to assess whether the criteria for a) Conduct Disorder (CD) or b) Oppositional Defiant Disorder (ODD) are met (yes/no). The results of the two disorders will be combined to one binary total score with 0 = no externalising disorder and 1 = current externalising disorder (ODD or CD).

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in Parent Daily Ratings (PDR): oppositional and aggressive sub scale (12 items), continuous sub-scale score

The primary outcome child oppositional aggressive behaviour is assessed with 3 indicators: 3) daily reports: The PDR oppositional and aggressive sub-scale (10 items) and 2 positive items will be used to monitor child behavioral problems. We excluded the last item from the scale ("he/she pouts") because this question caused translation problems in the three implementation countries during the last assessment. The item was not understood correctly by parents and assessors and thus did not result in valid answers. Parent will report on their child's behaviour within the last 24 hours (answer format: did occur/did not occur). The oppositional and aggressive subscale mean score will be calculating (score range: 0-1) with higher scores indicating more child problem behaviour within the last 24 hours. Additional exploratory analyses will include the mean score of the two positive items (range: 0 -1) with higher values indicating more frequent positive child behaviour.

PLH group: after the first, third and fifth session. lecture: after the lecture, 2 and 4 weeks later

Change in level of internalising problem behaviour in children: Child Behavior Checklist (CBCL) 11/2-5 (31 items) and 6-18 (32 items) parent-report, Internalizing Scale; continuous sub-scale score

The CBCL is part of the Achenbach System of Empirically Based Assessment (ASEBA) and is available for different age ranges, including the targeted range in the present study. For the present study, the parent-report versions for children aged 1½ - 5 and 6-18 are employed. It is the most widely used instrument for assessing child behavioral and emotional symptoms. In addition to the possibility to separate behavioral from emotional symptoms, the CBCL allows for assessment in multiple languages, including Romanian (all ages), Russian (all ages), and Macedonian (6-18 version). It is a very well validated instrument that has been used across different prevention and treatment studies. The internalising subscale raw score ranges from 0 to 62 (CBCL/1 ½ - 5 version) and 0 to 64 (CBCL/ 6 - 18 version) with higher scores indicating more emotional problems.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in frequency of dysfunctional parenting: Parenting Scale (PS) / self-report (shortened version); continuous total score and 2 sub-scale scores

This measure is widely used in parenting interventions across the world. The scale was designed to explicitly measure dysfunctional discipline practices in parents. Three subscales may be derived (Laxness, Overreactivity, and Verbosity). For phase 3, the subscale Verbosity is excluded due to poor performance in the pilot study, consistent with numerous other studies evaluating this subscale's psychometric properties. Each item is rated on a 7-point Likert Scale in which parents are presented with a situation and then are asked to choose between two alternative responses to a situation (1 = most effective; 7 = most ineffective; i.e., situation: "When I say my child can't do something"). For computation of the subscale scores as well as the total score, the responses on the items are averaged. We will use a modified total score (only from two subscales Laxness \& Overreactivity).

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in frequency of positive parenting and effective discipline: Parenting of Young Children Scale (PARYC) / self-report (21 items); continuous total score

Positive parenting behavior will be assessed using parent-report of the Parenting of Young Children Scale (PARYC, 21 items). The PARYC measures the frequency of parent behaviour over the previous month. Items are summed to create a total frequency scores parenting behaviour as well as for the sub-scales: positive parenting (7 items, e.g., "how often do you play with your child"), setting limits (7 items, e.g., "how often do you stick to your rules and not change your mind") and proactive parenting (7 items, e.g., "how often do you explain what you want your child to do in clear and simple ways"). This scale has been used in PLH trials in other countries and will allow comparison of results to those studies.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in daily report of effective parenting behaviour (5 items of Alabama Parenting Questionnaire), continuous score

We will use 5 items from the Alabama Parenting Questionnaire phone interview (3 items for positive and 2 for negative parent behaviours) to assess daily reports of parenting behavior. The original answer format was adapted to fit the PDR format (0=did occur/1=did not occur). One overall mean score will be calculated (ranging from 0 to 1) with higher scores indicating more effective parenting behaviour (ineffective parenting items will be reverse-scored).

PLH group: after the first, third and fifth session. lecture: after the lecture, 2 and 4 weeks later

Change in parent-child relationship quality as measured via FMSS (Five Minute Speech Sample) coherence; continuous total score

The FMSS assesses the caregiver's attitudes and feelings about the child and his/her perceptions of the quality of their relationship. The parent is instructed to talk about his/her child for five minutes. The parent-report is audio-recorded and rated by trained coders. The overall coherence scale ranges from 1 (not coherent picture of child) to 7 (very coherent picture of child) with higher scores indicating a more coherent narrative which indicates a better parent-child relationship. If inter-rater reliability of sub-scales is fair enough (ICC of .70 or higher), additional exploratory analyses will comprise the sub-scales concern / worry (1 "no worry and concern" to 7 "thematic concern and worry"), acceptance and warmth vs. rejection (1 "strong rejection" to 7 "high warmth and acceptance"), and separateness (1 "no clear separation" to 7 "complete separateness"; incl. boundary dissolution (BD) answer format: 0, 1, 2 with higher scores indicating more BD).

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in parent-child relationship quality as measured via FMSS (Five Minute Speech Sample) Family Affective Attitude Rating Scale (FAARS), sub scales Warmth and Criticism; continuous total score

The FMSS assesses the caregiver's attitudes and feelings about the child and his/her perceptions of the quality of their relationship. The parent is instructed to talk about his/her child for five minutes. The parent-report is audio-recorded and rated by trained coders. Parents are rated using two sub scales of the FAARS on 9-point Likert items ranging from 1 "no evidence for the duration of the speech sample" to 9 "two or more concrete, unambiguous examples of a particular behaviour or attribute" on each of 5 items per sub scale. Sub scale scores (mean of items): For the Criticism sub scale, higher scores indicate more negative attitudes (and thus a lower parent-child relationship quality); while higher scores on the Warmth sub scale indicate more positive attitudes (and thus a better relationship quality).

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in frequency and incidence of child maltreatment: ISPCAN-Child Abuse Screening Tool-Intervention (ICAST-I)/ self-report (16 items); main focus on continuous total score, 2nd question: any effect of intervention on any of the 3 sub-scale score

Child maltreatment (CM) will be measured using parent report of the ICAST-I, an adaptation of an instrument measuring parent-report of child abuse and neglect (ICAST-TC, Trial Children). The ICAST-TC measures four types of abuse: physical, emotional and sexual abuse, as well as neglect. The response code was adapted to a scale from 0 to more than 8 times to assess the frequency of a certain behaviour in the past month. This study will assess incidence of CM by creating dichotomous variables for physical abuse, verbal abuse, and neglect, as well as an overall indication of previous child abuse. We will also assess frequency of overall abuse by summing all of the subscales as well as for each individual subscale. Regarding emotional abuse, a 5-item-version is used. Sexual abuse is not assessed. If assessments cannot take place in-person (due to COVID-19 restrictions), this measure will not be administered during the phone assessment because of the sensitive nature of items.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in levels of psychological distress in parents: Depression, Anxiety, and Stress Scales - short version/ self-report (21 items); continuous total score

Depression, Anxiety, Stress Scales (DASS) will assess parent-report of psychological distress in parents, a 21-item scale used as a screening tool to measure depression, anxiety, and stress in adults. Caregivers report on the frequency of symptoms in the previous week using a Likert scale (0 = Never, 1 = Sometimes, 2 = Often, 3 = Always; e.g., "I felt that I had nothing to look forward to"). Total DASS scores range from 0 to 63 with subscales from 0 to 21. The DASS is a widely used measure across parenting studies including those of PLH-YC and will allow comparison to existing results of intervention studies in non-LMICs.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in levels of parenting stress: Parenting Stress Scale (18-items); continuous total score

The Parental Stress Scale measures parental stress across different domains (rewards, stressors, satisfaction, loss of control) with 18 items. An example, from the domain stressors, is "The major source of stress in my life is my child(ren)". Caregivers answer on a scale from strongly disagree (1) to strongly agree (5). The overall score ranged from 18 to 90 with higher scores indicating more parental stress.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in levels of parental relationship quality: Couple Satisfaction Index / self-report (4 items); continuous total score

This 4-item measure assesses relationship satisfaction among intimate partners. Items are summed to create a total score. CSI-4 scores can range from 0 to 21. Higher scores indicate higher levels of relationship satisfaction. CSI-4 scores falling below 13.5 suggest notable relationship dissatisfaction.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in levels of Intimate Partner Violence (29 items); continuous total score and 4 sub-scales (level of severity)

Intimate partner violence will be assessed with a screening instrument, the family maltreatment measure (Heyman et al. 2013) and an adaption of the revised Conflict Tactics Scale (CTS2S). The measure assesses adult self-report of perpetration and victimisation of intimate partner aggression. Assessments measure the frequency of negotiation, physical assault, psychological aggression, and physical injury. This measure indicates an overall indication of IPV on a level of severity (sum of items) and prevalence (dichotomous variable indicating experience of conflict or not) as well as for each subscale. Only severity is examined here. For the current study a 9-point Likert scale of 0 to 8 is used, with an additional response for incidences that happened but not in the past month. If assessments cannot take place in-person (due to COVID-19 restrictions), this measure will not be administered during the phone assessment.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

Change in Child Quality of Life: Child Health Utility 9D (CHU9D; 9 items); continuous total score

The CHU9D measures parent-reported child health-related quality of life. The questionnaire consists of nine dimensions (worried, sad, pain, tired, annoyed, schoolwork/homework, sleep, daily routine, activities) with five levels (e.g., 1 = "don't feel worried"; 5 = "very worried"). Higher scores indicate lower levels of quality of life. The scores of the CHU9D range from 9-45.

pre: Jan/Feb 2021; post: approx. 4 months after pre assessment (May/June 2021); follow-up: approx. 10 -12 months after pre-assessment (Dec 2021 - Feb 2022)

RE-AIM Reach: Enrollment rate

Total number of caregivers who attend the first session of the PLH/ the lecture group divided by the number of families recruited in that condition).

approx. 4 months after pre-assessment (May/June 2021)

RE-AIM Reach: Participation rate

Only for caregivers that were allocated to the PLH condition: percentage of sessions attended out of the 5 sessions

approx. 4 months after pre-assessment (May/June 2021)