Good health and wellbeing are essential for all children to have the best start in life. Early childhood is the most critical and rapid period of development and provides the foundation for an individual’s acquisition of health behaviours. Physical activity and healthy nutrition are two important contributors to a child’s health, with evidence that these factors impact mental and physical health and psycho-social wellbeing. Lifestyle changes for children in industrialised countries have resulted in altered physical activity levels and food consumption patterns. The combined effect of these changes has important implications for children’s health status, with the complex interplay of factors contributing to adverse consequences on a population level. Given the importance of physical activity and food intake in early childhood, it is crucial from a public health perspective to understand how and why these behaviours are formed. Social-ecological theory posits that a child’s activity and dietary behaviour result from an interaction between personal characteristics and contextual conditions. This suggestion has been supported by the robust finding that individual characteristics and contextual conditions work together to directly shape child health and health behaviours. This interaction is borne out in circumstances where a child’s understanding of health and health behaviours and their own personal preferences in regard to food and physical activity combine with environmental factors to shape lifestyle behaviours. This program of research focuses on children’s understandings of health and of factors which shape their knowledge of and preference for food and physical activity. The need to incorporate children’s perspectives in the development and delivery of health education and interventions has emerged as a key theme within the contemporary child health literature. The growing recognition of preschool children’s agency in determining their own health behaviours has triggered a need to better understand their perspectives regarding how they and/or others make health choices for them. Gaining a child-centric view may help to identify overlooked aspects of the environment that influence lifestyle preferences. To date, limited research has investigated preschool children’s knowledge of and preference for health behaviours, the contextual factors that may impact these variables and how this translates into health behaviours. The aim of this program of research was to address these gaps in current literature. This thesis incorporates six research studies designed to address the overall research aim. Each of the six studies build on each other to enable a deeper understanding of factors shaping children’s knowledge and preferences for lifestyle behaviours. The findings have been published or are under review in peer-reviewed journals. This research was underpinned by the pragmatic paradigm in order to accommodate the use of a mixed methods approach where the researcher collects, analyses, and integrates both quantitative and qualitative data in a single study or in multiple studies in a sustained program of inquiry. A conceptual framework was developed to guide this research. Study 1 was a systematic review of the literature that aimed to identify and review data collection techniques used to measure preschool children's knowledge of food and nutrition. Twenty studies met the inclusion criteria and were critically appraised. The findings of this review identified the need for additional research to develop valid and reliable measures of preschool children’s food and nutrition knowledge. Prior to implementing and evaluating a nutrition program, assessment tools need to be pilot-tested, refined, and adapted to suit both the specific audience and the components of the nutrition knowledge being targeted. The findings of this review have been published in a peer-review academic journal and informed the development of Study 3. Study 2 was a systematic review of the literature that aimed to identify and review data collection techniques used to measure preschool children's knowledge of and preference for physical activity. Fourteen studies met the inclusion criteria and were critically appraised. The identified studies employed a limited but disparate range of techniques to assess children's physical activity knowledge and preferences and highlighted a need for validated and reliable measures to assess these variables. The review highlighted that greater consideration is required to align data collection techniques with the needs and abilities of the study population. This study has been prepared for submission to a peer-review academic journal and informed the development of studies three and five. Study 3 was a validation study that assessed the reliability and validity of an adapted computerised (iPad) version of the photo-pair food and exercise questionnaire (PPFEQ). A cross-sectional design was used to incorporate four phases of quantitative investigation, including interviews at four time-points with 86 preschool children, to assess test-retest reliability, internal consistency, sensitivity to change and percent agreement of the questionnaire. The adaption of the PPFEQ resulted in an 18-item questionnaire, titled the Preschool Food and Play Questionnaire [Pre-FPQ]. The Pre-FPQ demonstrated acceptable reliability and sensitivity to change. Test-retest reliability and internal consistency improved with age, though it was evident that the tool was not suitable for children younger than four years of age. The findings of this study have been published in a peer-review academic journal and informed the development of studies four, five and six. Study 4 included a qualitative cross-sectional study that included 163 preschool children who participated in one-on-one semi-structured interviews. The aim of this study was to explore how preschool aged children speak about health and health behaviours. Findings highlighted the centrality of food in how children speak about health. In contrast, there was limited mention of physical activity as a way to be healthy. The theme ‘reduce risk’ emerged from participant responses and relates to the practice of safety behaviours to prevent injury and illness. The findings of this study have been published in a peer-review academic journal and informed the development of studies five and six. Study 5 was a qualitative, cross-sectional study that included 40 preschool children who participated in one-on-one semi-structured interviews. The aim of this study was to explore preschool children’s preferences for physical activity and barriers and facilitators to participating in these activities. Participants expressed preferences to play unstructured activities with friends or family, to engage in imaginative, challenging play, as well as to have control over the activity they engage in. Children reported that rules at home and at preschool, the availability of toys, friends, family and having access to a natural environment served as both barriers and faciliators to participating in their favourite activity. This study was prepared in a manuscript format (Manuscript 5), has been submitted to a peer-review academic journal and informed the development of Study 6. Study 6 was a quantitative study that included 138 parent-child dyads. Parents completed a questionnaire that comprised demographic questions, questions regarding their child’s physical activity/sedentary behaviours and parenting practices thought to influence children’s physical activity and inactivity (e.g. screen time behaviours). Children were asked to complete the Pre-FPQ, which measured children’s knowledge of and preference for physical activity. The results of parent and child questionnaires were matched. The findings of this study revealed that children’s preferences for physical activity were correlated with a number of demographic characteristics and physical activity parenting practices, with the most influential variables being parental age, parental rules around active play outdoors and parental use of screen time to reward/control child behaviour. Children who preferred to be physically active were more likely to engage in physical activity and were less likely to engage in screen time on the weekend. This study was prepared in a manuscript format (Manuscript 6) and submitted to a peer-review academic journal. Collectively, the findings of this research program highlighted the benefits of using age-appropriate techniques to involve children in the research process, and how this process can offer important insights into their world. This research identified ways in which active play can be made more enjoyable to preschool children, which may allow children to develop a more positive relationship with physical activity. Finally, this research identified the relationships between demographic factors, physical activity parenting practices and children’s activity preferences and behaviours. The findings from this research can inform public health professionals, educators and researchers of the importance of considering contextual factors that shape children’s knowledge of and preference for healthy lifestyle behaviours and provides recommendations for further action and research. Early childhood is undeniably a crucial life stage that influences health outcomes throughout the life course. How we act to promote health during this life stage may therefore hold the potential to dictate the health challenges of our future society.