Worldwide, Youth Health Care (YHC) is part of social medicine aimed at young people and YHC is population based (World Health Organization [WHO], 2018). In Europe, each country organizes YHC in a different way (Wieske et al., 2012). In the Flemish part of Belgium and the Netherlands, YHC, is defined as preventive care which protects, monitors and promotes growth and development of children and adolescents at a physical, cognitive and social emotional level. YHC aims to enable all children and adolescents to grow up to become adults who give meaning to life and who can take up their role in society (Van Hoeck et al., 2010). To achieve this goal, early assessment and detection of child developmental and parenting problems is an important task for YHC professionals such as YHC nurses (European Union for School and University Health and Medicine [EUSUHM], 2019; Hermanns et al., 2005; Van Hoeck et al., 2010), because required interventions are assumed to be more effective when they are carried out earlier (Hertzman et al., 2010; National Early Childhood Technical Assistance Center (NECTAC), 2011; Tollan et al., 2023). Another important reason to invest in early detection and intervention, is that this is in line with the Rights of the Child (United Nations Children's Fund [UNICEF], 1989), based on a United Nations convention which is ratified by all European countries. To establish early detection of child development and parenting problems, the assessment is preferably done with a valid and reliable instrument.

In the past, standardized tools were developed to assess child development or parenting, for example the Ages and Stage Questionnaire (ASQ) (Squires & Bricker, 2009), the Strength and Difficulties Questionnaire (SDQ) (Goodman, 1997), the Parenting Stress Index (PSI) (Abidin, 1995), the Questionnaire Family and Parenting (in Dutch: Vragenlijst voor Gezin en Opvoeding (VG&O)) (De Meyer et al., 2011). However, none of these instruments address a broad scope of development and parenting. Therefore, a broad scope structured instrument named ‘Structured Problem Analysis of Raising Kids’ (SPARK) has been developed in the Netherlands for use in the preventive YHC (Staal et al., 2011). This instrument aims to improve early detection of child developmental and parenting problems and to reduce the differences between YHC nurses' assessments. The SPARK facilitates a structured conversation with parent(s) and includes 16 domains covering the child, the family and the child-rearing environment. In brief, the method is used to assess parents' concerns and need for support, combining the perspectives of the parents (as professional of their child) and the YHC nurse (as professional of normal development). It aims at providing aftercare based on the experienced parental needs, based on the shared decision of parents and YHC nurse, and based on the assessment of the risks of child developmental and parenting problems. The SPARK instrument is available for YHC nurses who offer preventive consultations to parents of children at significant transition moments: SPARK18 for children aged 18 months, SPARK60 for children aged 60 months and PreSPARK for use during pregnancy. These transition moments are important moments in the life course, as they related to developmental tasks for children and parenting tasks for parents (Staal et al., 2011). They signify important changes in child development and parenting, such as preparing for the role of a parent, starting school, entering adolescence, or adapting to a new social environment. During these times, children acquire new skills and face challenges crucial for their growth, while parents simultaneously adjust their parenting strategies to support their child through these transitions. Monitoring these moments can enhance both the child's and the family's resilience, promote healthy development, strengthen family dynamics, and facilitate early detection of developmental and parenting issues. The psychometric properties of the SPARK have been evaluated in several ways: the validity, reliability and feasibility of the SPARK have been shown satisfactory in other studies (Staal et al., 2011; Staal et al., 2013; Staal et al., 2015; Staal et al., 2016; Van der Put et al., 2023; van Driessche et al., 2021; van Stel et al., 2012). Recently, a SPARK for children at the age of 36 months (SPARK36) has been developed (Keymeulen et al., 2021), as in Belgium, this is an important transition moment in life from being a toddler to being a pre-school children. It is based on the SPARK18 and SPARK60 versions and has been adapted for use in the Flemish YHC in Belgium. More specifically, it was developed for nurse-led consultations with three-year-olds and their parents, as organized by the School Health Services (SHS). Since a new legislation on SHS in Flanders has been introduced in 2018, all children and their parents are invited for a preventive consultation in the first year of nursery school (at age 3). Having a conversation with the parent during this consultation and making a risk assessment for child development and parenting problems (based on the conversation, biometrical tests and the observed interaction between child and parent) is a new assignment for which no (valid) instrument was available. SHSs, or more specifically 749 YHC nurses, are needed to organize these consultations for the nearly 70,000 three-year-old school-age children in Flanders. However, the new legislation does not describe how these consultations should be organized. As a result, there is a lot of variation in how the consultations with three-year-olds and their parents are conducted, aiming at risk assessments for children's developmental and parenting problems (De Bolle, 2017). This variation motivated the search for a reliable and valid tool to guide the new assignment in a standardized, uniform and effective manner.

Since the SPARK36 is an adapted version of the SPARK18 and SPARK60 for use in a different context at a different age, it is relevant to assess the psychometric properties of the SPARK36. Therefore, several studies regarding the SPARK36 on feasibility and known-groups validity have been conducted already (Keymeulen et al., 2021: Keymeulen et al., 2023). These studies showed satisfactory results. Additionally, an instrument’ ability to demonstrate similar results by different raters is a critical aspect of its quality. Therefore, our current aim is to evaluate the interrater reliabilityof the SPARK36.