**3. A Dimensional Framework of Child Functioning and Development**

Epidemiological studies on the nature and extent of developmental problems of young children globally [3,8,9] reveals that using indicators such as being disadvantaged, at risk for developmental delay and/or experience loss of developmental potential may account for prevalence estimates ranging from 19% to 51% in countries across income levels. Prevalence estimates vary based on the nature of the indicator, from proxy variables of stunting, poverty status, wealth inequalities to caregiver report of the child's medical condition, health care needs or social and academic skills. Of note is the large variability of children's risk of poor development between world regions and low and middle-income countries within regions, ranging from 7% to 73% [9]. The role of environmental factors on children's poor development is evident in the variability of prevalence of risk paralleling variability in the status of economic development of countries. Perhaps the strongest reflection of the role of the home and community environment placing children at developmental risk is high level of suspected developmental delay in literacy-numeracy, across the seven world regions, ranging from 56.3% to 87% [12]. Although the studies utilized different indicators to document developmental risk, the findings provide a consistent picture of problems and

delays of development in up to half of all children 3 to 5 years of age growing up in low and middle-income countries. Lower, but comparable prevalence estimates of developmental delay and elevated health care needs in higher income countries supports the premise that developmental risk is a universal concern for young children with implications for policy and practice in the form of SDGs as well as regional and national initiatives.

The gradual decline in the prevalence of children at developmental risk in recent decades with estimates declining from about half to slightly less than 40% of the population in low and middle-income countries [9] has been documented even in the context of variability in how developmental risk was identified. Variability in prevalence estimates may reflect the conceptualization of developmental risk as well as the specific way in how the target problem was defined and cases identified. Different terms defining the population of interest such as "loss of developmental potential " [8], "disadvantaged children" [9], or "risk for developmental delay" [12] reflect different conceptual and assessment criteria and may thus account for some of the variability of prevalence estimates. However, there is correspondence of these overall prevalence estimates supporting the premise of common, underlying factors of developmental risk. When a more specific definition such as "literacy-numeracy delay" [11] with an associated Literacy-Numeracy Index (LNI) was used in a survey of 35 low and middle-income countries, mean prevalence estimate of children not meeting the criteria for being on-track of LNI was 70.1%, with large variability across countries, ranging from a low of 10.1% to 94.3%.

Although the succession of prevalence estimates over recent decades provides overall documentation of the scope of children at developmental risk, differences in the identification of risk yields different implications for policy and practice. In part, differences in the identification of risk may reflect trends in moving from the use of proxy indicators (e.g., stunting and poverty), subgroup designations (e.g., disadvantaged children) to more specific dimensions of developmental delay (e.g., social-emotional development; literacynumeracy development). Comprehensive initiatives for children have been listed in term of goals in the MDG and SDG as the basis for defining earlier studies, but an integrated, conceptualization of the developing child within limiting or facilitating environments has been lacking in defining the focus of studies. The importance of a conceptual framework integrating components of child development within a life-course perspective to promote early development of children in low and middle-income countries has been advanced by Black et al. [7]. Central to their approach is the promotion of the child's developmental potential across the life-course through the provision of nurturing care for health, nutrition, security and safety, responsive caregiving, and early education. Implementation of such an approach recognizes the facilitating role of the systems and policy environment and the caregiving environment of family and community.

Within the ongoing commitment to advance the SDGs for children, a conceptual framework is needed that captures the dimensions of the child's interaction with the environment defined by the SDG 4 target indicators for early childhood development 4.2, 4.2.1 and 4.2.2. Specifically, the emphasis of the target indicators on children's access to, and participation in, nurturing and learning environments to ensure their rights to health, learning and well-being requires a conceptual framework integrating dimensions of the child's developmental interactions with the environment. Central to that framework is a view of early development as the product of the child's ongoing interactions with the physical, social, and attitudinal environments. The significance of these interactions in defining developmental trajectories and different outcomes of children has been defined in the transactional model of Sameroff and Fiese [19] in which reciprocal child-environment interactions account for developmental change. A similar approach has been proposed by Batorowicz et al. [20] emphasizing transactions as the important feature for interventions for young children. Drawing on the transactional approach, elements of the child-environment interaction need to be defined in dimensional terms of characteristics of the child, of the environment and of the interactions of the child with the environment. To that end, the ICF-CY [4] offers a dimensional taxonomy and accompanying codes of body functions

(8 chapters), body structures (8 chapters), environmental factors (5 chapters), and activities and participation (9 chapters), well suited to document the characteristics of the child, the environment and child-environment interactions, respectively.

Drawing on the findings of the above prevalence studies, the variable or variables defining children's developmental risk or loss of developmental potential can be identified as elements of the child's interaction with the environment as shown in Figure 1. Approaching prevalence studies within a framework incorporating the ICF-CY may be useful in several ways [6] in that it promotes focusing on developmental risk in interactional terms rather than solely as characteristics intrinsic to the child. As a universal classification, the ICF-CY codes offer a common language integrating data collection and analysis in health and education sectors that may differ across countries. Further, the codes address the need to assess child, environment and interaction variables in a standard manner across time, for example, in specific contexts such as special education services in Portugal [21] and in broader applications for documenting intervention outcomes in low-and middle-income countries [22].

**Figure 1.** Interactional framework—modeling child-environment interaction within International Classification of Functioning, Disability and Health for Children and Youth (ICF-CY) domains.
