## 2 Review of Related Literature and Applications  
### Current Trends in Smart Device Usage and Developmental Impacts on Young Children  
With the widespread adoption of smart devices, digital media usage among young children has become a subject of increasing academic and societal concern [6]. A large corpus of research has explored its impact across multiple dimensions of early childhood development, including language acquisition, social interaction, physical health, cognitive growth, and emotional well-being. While digital media can offer educational benefits, prolonged or unregulated use has been associated with a range of developmental risks, underscoring the importance of parental guidance and the need for age-appropriate design strategies [7].  
In response to these concerns, the World Health Organisation (WHO) has issued recommendations for healthy screen use in early childhood [8]. These guidelines advise that children under the age of two should not be exposed to digital screens at all, while those aged between two and four should be limited to a maximum of one hour of screen time per day, with an emphasis on physical activity and sufficient sleep [8]. Nevertheless, studies indicate that these recommendations are frequently disregarded--especially following the COVID-19 pandemic, during which preschoolers' screen time increased substantially as parents turned to digital media for both childcare and entertainment [9,10].
* Physical Health  
Extended screen exposure has been reported to reduce physical activity among children, increasing the risk of obesity and hindering motor development [7]. It has also been associated with visual impairments, including eye strain and long-term vision problems. Moreover, the use of smart devices has been linked to sleep disturbances, such as shorter sleep duration and poorer sleep quality, both of which may adversely impact developmental outcomes [11].
* Cognitive and Language Development  
Early and excessive exposure to digital devices can adversely impact cognitive development. Several studies have linked prolonged screen times to delayed language acquisition [12, 13, 14], which may, in turn, influence academic performance in later stages. Moreover, the fast-paced, reward-driven nature of digital media has been speculated to reduce attention spans and impulse control among young children [15]. However, when digital content is well designed and used alongside parental involvement, it can support language development and enhance problem-solving skills [16,17].
* Social and Emotional Development  
Smart device use also carries important implications for social and emotional development. Research demonstrates that parental smartphone use during interactions with young children can reduce sensitivity and responsiveness, thereby weakening the parent-child relationship [18]. Excessive screen exposure may further limit face-to-face peer interaction, potentially hindering social competence [19,20]. Moreover, frequent and unsupervised use of smart devices during adolescence has been associated with social withdrawal and difficulties in establishing interpersonal relationships [21]. Conversely, some studies suggest that interactive digital platforms--when used collaboratively with parents--can foster family bonding and even support the development of social skills [22].  
In summary, smart device usage in early childhood exerts complex influences on physical, cognitive, emotional, and social development. Although the adverse effects frequently outweigh the benefits, complete avoidance of digital media is unrealistic within the context of modern parenting. As such, a balanced approach that mitigates negative outcomes while fostering developmentally appropriate media engagement is essential. The following section reviews strategies that have been proposed to guide and regulate smart device usage among young children.