Typically, 3-6-year olds are estimated to require around 10-12 hours of sleep per day (The Sleep Council, 2019). This is thought to be essential for healthy growth and wellbeing, and is significantly associated with predictors of adult health (Bathory \& Tomopoulos, 2017). Sleep disturbances and difficulties are found to be highly prevalent amongst infants and young children (Honaker \& Meltzer, 2014). The literature estimates between 25% to 50% of pre-school aged children get too little sleep (Owens \& Mindell, 2011), and a quarter of parents report sleep difficulties in their child's first five years of life (Bathory \& Tomopoulos, 2017). This is a concern as evidence suggests early childhood to be a critical time for establishing sleep habits which have implications for sleep quality throughout the lifespan (Bonuck, Blank, True-Felt \& Chervin, 2016). Research also shows a well-established link between sleep and long-term health outcomes for children. A recent review shows poor sleep to negatively effect physical health factors such as weight problems, as well as cognitive development, cognitive performance and behavioural functioning (Spruyt, 2019). Thinking more broadly about the impact on families, sleep problems in children have been found to impact the quality of maternal sleep, which then acts as a significant predictor of maternal mood, stress and fatigue (Meltzer \& Mindell, 2007). Mindell and Williamson (2018) highlight that investing in not only interventions for disordered sleep but preventative strategies to promote healthy sleep is therefore essential in promoting positive health outcomes for children and their family systems.

Implementing sleep hygiene practices with children has been found to be positively associated with better sleep across a range of ages (Mindell, Meltzer, Carskadon \& Chervin, 2009). Sleep hygiene can be defined as a set of specific behaviours and activities that are conducive to increasing healthy and adequate sleep (Perlis, Smith \& Pigeon, 2005). This includes the consideration of factors such as environmental noise, bedroom environment, light exposure, exercise, temperature and electronic device use (Richdale \& Schreck, 2019). Mindell and Williamson (2018) also suggest appropriate communication and contact with carer as an important aspect of sleep hygiene. The literature suggests that such techniques should be encompassed within a regular and structured bedtime routine to be most effective. Following a bedtime routine is associated with positive sleep outcomes; such as earlier bedtimes, increased sleep duration, reduced night time awakenings and reported caregiver sleep quality (Mindell and Williamson, 2018). Such outcomes have been observed in as little as two weeks from implementing sleep hygiene practices (Mindell, Leichman, Lee, Williamson \& Walters, 2017). Encouraging bedtime routines that include sleep hygiene practices could therefore be a cost-effective way to promote positive childhood sleep outcomes, which could then have beneficial effects on a broad range of child development factors. Despite this, research suggests that caregiver knowledge in regards to their children's sleep habits is poor (McDowall, Galland, Campbell \& Elder, 2017). Studies have shown increased knowledge of sleep hygiene to be associated with an increased number of positive sleep practices and increased sleep duration in young children (Owens \& Jones, 2011). It has therefore been suggested that caregiver education on sleep hygiene could be used as a first line intervention for sleep problems in young children (McDowall, Galland, Campbell \& Elder, 2017). This indicates that preventative interventions and resources for childhood sleep problems would likely benefit by including a degree of caregiver education.

Evidence-based interventions to promote healthy sleep habits in young children have largely focused on sub-groups of children and so may not be transferable to the general population (Busch, Altenburg, Harmsen and Chinapaw, 2017). For example, sleep interventions have been developed for children with autistic spectrum condition (Johnson et al., 2013; Turner \& Johnson, 2013), intellectual disabilities (Stuttard, Beresford, Clarke, Beecham \& Curtis, 2015), children with lymphoblastic leukaemia (Zupanec, Jones, McRae, Papaconstantinou, Weston \& Stremler, 2017), those with specific sleep difficulties (Schlarb \& Brandhorst, 2012; Kuhle, Urschitz, Eitner \& Poets, 2009), as well as children living in socioeconomic adversity (Caldwell, Ordway, Sadler \& Redeker, 2020; Ordway et al., 2020). In terms of interventions for the general population to promote healthy sleep, Busch, Altenburg, Harmsen and Chinapaw (2017) provide a review of those developed for children aged 4-12 years. They conclude that due to few high-quality studies, the effectiveness of any specific intervention strategy is inconclusive. They recommend the need for further evaluation of systematically developed interventions to encourage positive sleep habits in children. This current study's investigators argue the need for further research evidence examining which methods are effective in promoting healthy sleep in pre-school aged children, to then aid the development of widely accessible evidence-based resources.

Resources (e.g. storybooks, games) designed to be used with young children before bed are widely available. However, the efficacy of these in terms of promoting positive sleep outcomes relies mainly on anecdotal evidence from carer in the form of online reviews and blogs. Resources that have been evaluated in research for this age group tend to be in the form of educational interventions rather than ones that can be used at home. For example, the 'Sweet Dreamzzz Early Childhood Sleep Education program (Wilson, Miller, Bonuck, Lumeng \& Chevrin, 2014) was developed for pre-school children and parents. This included a one-off workshop for parents and a two-week classroom curriculum for children to help establish bedtime routines involving positive sleep hygiene activities. Results included an increase of 30 minutes per night for children's sleep at one-month follow-up and increased parental knowledge of sleep hygiene practices; though this effect was not lasting. Schlarb and Branhorst (2012) developed an internet-based intervention, 'Mini-KiSS Online', for sleep disturbances in children aged 6-months to 4-years and their parents. Parents attended six online intervention sessions which included psychoeducation on sleep and implementing strategies to promote sleep hygiene including; imaginational exercises, bedtime stories, improving sleep environment; cognitive-behavioural techniques and relaxation exercises. Results indicate the intervention was highly accepted by parents and included improvements in falling asleep, less night time awakenings and less bedtime resistance. Though effect sizes were small to medium and results were limited by a high dropout rate (46%). Educational treatment programs rely on carer to independently implement learnt techniques which may be a reason for high dropout rates, as well as a high variation in how the strategies are implemented. This suggests that carer may benefit from resources they can use within the home, to help scaffold the bedtime routine and promote sleep hygiene activities in 'real time' with their children.

In terms of an evaluated resource that can be used at home, one study evaluated the game 'Perfect Bedroom: learn to sleep well'. This is a digital interactive game for 7-9-year olds, which encourages children to map out their bedtime routine to include sleep promoting activities and limit negative sleep hygiene activities such as the use of electronic devices. Preliminary results indicated the potential for this tool to be effective in promoting healthy sleep habits (Almondes \& Leonardo, 2019), though the sample size was small (n=13). The authors also described this as the first study that used a 'serious game' (game designed for a primary purpose other than entertainment) to promote healthy sleep habits in children. In terms of study's evaluating serious games that promote healthy sleep habits for a younger age group in the home environment, this current project would therefore be the first to our knowledge to do so.

The literature highlights a need for the development and evaluation of evidence-based preventative resources that can be used at home as part of a child's bedtime routine. This study aims to provide a resource that pre-school children can play before bedtime with carers; in which they follow the characters on a journey through a fictional land, helping its inhabitants get a good night's sleep along the way. This will work by incorporating and encouraging positive sleep hygiene practices and relaxation exercises. It will include evidence-based practices shown to aid relaxation, using elements of mindfulness, deep breathing, imagery techniques and muscular relaxation. It will also include soothing activities and an appropriate level of child-caregiver interaction. The intervention is novel in that it aims to support children's sleep practices within the home environment, and therefore will have strong ecological validity. This research project therefore aims to develop and evaluate the sleep resource on a range of outcomes for both children and carer when played regularly together before bedtime.