## 2 Review of Related Literature and Applications
### Limitations of Existing Research and Market Solutions and the Need for a New Approach  
Although commercial implementations offer a range of solutions informed by prior research, they seldom succeed in translating developmental principles into user experiences that are truly appropriate for preschool-aged children. Many tools remain centred on rule enforcement and external monitoring, with limited support for fostering children's intrinsic capacity for self-regulation. Academic literature similarly focuses on parental control, co-use mediation, or algorithmic restriction--approaches that, while useful, often fail to reflect the emotional, symbolic, and autonomy-related needs of young children. Parent-centred strategies are often based on fixed rules--such as screen time limits or app restrictions--that may prompt avoidance behaviours or reduce children's emotional engagement. In contrast, collaborative methods such as co-use and guided mediation require sustained adult involvement and digital literacy, which may not be feasible across all families. Although technology-based interventions offer scalability, they often function as external control systems, rather than as tools to cultivate internal behavioural awareness. Additionally, many existing tools are designed for school-aged children or adolescents and do not adequately address the distinct developmental profiles of preschoolers. Such systems often overlook symbolic reasoning and emotional scaffolding--cognitive capacities that are especially important for designing self-regulation strategies in early childhood. Recent studies have begun to explore affective UX approaches that incorporate narrative structure, emotional prompts, and symbolic interaction to improve engagement and promote voluntary transitions. These include strategies such as bedtime routine animations, gentle screen dimming, or empathetic voice prompts that create emotionally meaningful closure experiences [54; 55; 56]. While these directions are promising, they tend to appear in isolated design features and lack integration into cohesive UX models. Therefore, there remains a need for a structured design framework that applies developmental psychology principles--such as children's responsiveness to symbolic cues, their need for emotional guidance, and their preference for ritualised transitions--to UX systems aimed at supporting early self-regulation. The limitations discussed above have prompted recent research into alternative ways of promoting digital self-regulation in early childhood. Empirical studies have proposed design strategies that emphasise emotionally grounded and autonomy-supportive interactions. For instance, [PERSON] et al. demonstrated that transitions framed in an emotional context--such as the use of anthropomorphic characters to signal the end of screen time--were more effective than conventional countdowns in reducing resistance [55]. Similarly, [PERSON] and [PERSON] found that augmented reality prompts embedded in family routines significantly improved the success rate of transitions [56]. Another study by [PERSON] et al. comparing digital and analog play highlighted the role of joint engagement in improving cooperation during transitions [54]. Together, these findings emphasise the importance of affective design elements, time-awareness cues and child agency in fostering self-regulation. Concurrently, research on tangible user interfaces (TUIs) and participatory design frameworks--particularly [PERSON]'s Cooperative Inquiry model--has emphasised the value of embodied interaction and the inclusion of children as active contributors in technology design [57]. While the present study does not directly engage children as co-designers, it reflects participatory values by integrating developmentally informed perspectives throughout the design process and iteratively refining the UX framework based on expert consultation.