1. Introduction

In recent years, with the acceleration of China's urbanisation process, a large number of rural laborers have flocked to the cities to work, resulting in a surge in the number of rural left-behind children [1]. Left-behind children are minors under 18 whose parents migrate for work, leaving them in rural areas for over six months, typically cared for by one parent, grandparents, relatives, neighbors, or peers [1]. Long-term parental absence significantly affects the mental health of left-behind children, raising substantial social concerns. Current research extensively examines their mental health, emphasizing ability development, internalized psychological issues, and externalized behavioral problems. Findings indicate that parental presence is crucial for academic growth, and the absence of both parents can negatively influence academic performance through increased depression and decreased learning engagement [2]. In addition, the current state of left-behind children's mental health is also worrying, with left-behind children more prone to psychological problems and behavioral deviations than non-left-behind children. Research indicates that left-behind children face increased risks of depression, anxiety, and behavioral issues due to prolonged parental absence, with a significantly higher prevalence of emotional and behavioral problems compared to non-left-behind peers [3]. Compared with non-left-behind children, left-behind children are more likely to exhibit externalising behavioural problems, with aggressive behaviour being particularly prominent [4], and the lack of a supportive family environment significantly increases the risk of behavioural problems [5].

Existing research inadequately addresses the theoretical mechanisms underlying the mental health issues of left-behind children. This paper aims to elucidate these mechanisms, integrating theoretical analysis with case studies, and proposing targeted intervention strategies. The findings are intended to inform the development of effective mental health policies, ultimately enhancing the well-being of left-behind children and contributing to social stability.

2. Theories

2.1. Parenting and Care Theory

The theoretical foundation for the developmental delays in left-behind children stems from the nurturing care framework. This comprehensive model encompasses health, nutrition, safety, responsive care, and early learning, offering critical insights into the interplay of factors influencing child development. Studies indicate that optimal developmental potential is contingent upon a stable environment fulfilling children's health, nutritional, protective, educational, and emotional needs [6]. Nurturing care not only regulates the development of key brain regions but also promotes children's developmental adaptations, enhances social cooperation, reduces violent tendencies, and lays the foundation for their lifelong development [7]. Left-behind children frequently experience inadequate parental care due to prolonged parental absence, leading to substantial deficits in language, cognitive, and socio-emotional development. They are often reared in settings lacking adequate early learning opportunities and positive emotional engagement, which subjects them to stress and adversity, adversely impacting their learning capacity, academic performance, and social involvement.

2.2. Attachment Theory

For the development of children's competence, attachment theory emphasises that the establishment of secure attachments between children and significant others (e.g., parents) is essential for their functional development in different areas of life, including academic performance [8]. Secure attachment fosters emotional security in children, facilitating exploration and support-seeking during challenges. For left-behind children, extended parental absence can hinder secure attachment, negatively impacting adaptability and academic performance. Those without secure attachments may experience increased anxiety, heightened loneliness, and reduced learning engagement, ultimately constraining their development.

Attachment theory posits that the quality of a child's interactions with caregivers significantly influences attachment styles and behavioral development. Insensitive, unresponsive, or rejecting caregiving can foster insecure attachments, marked by uncertainty and negative emotions. Consequently, children may exhibit increased aggression, diminished prosocial behavior, and inadequate social skills, adversely impacting their interpersonal and social adjustment [9]. Due to the lack of emotional support and sensitive responses from their parents, left-behind children may have difficulty establishing a sense of trust and security and thus show more negative emotions and behavioural problems in social interaction. For example, they may cope with social stress through relational aggression (e.g., exclusion, and isolation of others), which further exacerbates their adjustment difficulties at school and in peer groups.

2.3. Emotion Regulation Theory

Emotion regulation theory explores the critical role of emotion regulation in an individual's early development and its far-reaching impact on subsequent social and emotional development. During the first year of life, carers (e.g., parents) play a crucial role in the formation of children's emotion regulation skills. Parents help children learn to recognize, understand, and regulate their emotions by providing emotional support, guidance, and modelling. However, if parents fail to provide adequate guidance and support, children's emotion regulation skills may be negatively affected, which in turn affects their social and emotional development [10].

Research has shown that emotional dysregulation not only affects an individual's mental health but may also lead to social and behavioural problems [11]. When children struggle to regulate their emotions during stress or provocation, they may resort to relational aggression, a behavior that manifests anger or distress through manipulation of others' relationships. This is prevalent among those with poor emotional regulation and can damage interpersonal connections while intensifying their emotional turmoil, perpetuating a harmful cycle [12].

From the perspective of developmental psychology, the development of emotion regulation is a gradual process, and early parent-child interactions provide children with a ladder for learning emotion regulation. Parental sensitivity and responsiveness are particularly important in this process. When parents can identify and respond to children's emotional needs promptly, children gradually internalise these regulatory strategies and apply them to a wider range of social situations. Conversely, if parents ignore or misunderstand children's emotional expressions, children may feel confused and helpless, thus inhibiting emotional expression and struggling to develop effective emotion regulation skills [13]. In addition, the development of emotion regulation skills is closely linked to cognitive ability. As children's cognitive skills advance, they better comprehend emotional complexity and employ sophisticated strategies for regulation. For instance, older children may manage emotional distress through reappraisal or social support instead of resorting to aggression.

3. Case Study

3.1. Bullying of Handan's Left-behind Children

A bullied child died in Laodian, Hebei Province, near Handan in March 2024. The village's 13-year-old junior high school student Wang Xiaojun was slain by three minor classmates. A reporter visited the village where the victim and three suspects live and discovered they are all left-behind children. Wang Xiaojun's family is good, and his father, who works outside the home, sends him pocket money. Before the murder, the three school performance suspects were not delinquent youths and often played with the victim, which let instructors and parents miss the underlying contradictions and dangers.

In this case, as a left-behind child, the victim, Wang Xiaojun, lacked direct parental companionship and emotional support for a long time. Due to parental neglect, he failed to obtain effective guidance and protection when facing interpersonal conflicts or bullying. At the same time, he did not have the energy in his heart to cope with the conflicts and the guts to resist.

Analysing the three suspects from the perspective of attachment theory, as left-behind children, they also lacked parental love and care in their growing environment and may have established insecure attachment relationships. The absence of secure attachment relationships resulted in emotional isolation and insecurity, hindering their ability to form healthy peer connections. While they may have engaged in play with the victim on the surface, they likely harbored unresolved conflicts and negative emotions beneath the surface.

According to emotion regulation theory, the three suspects experienced insufficient parental support and guidance during the crucial phase of emotion regulation development, potentially hindering their ability to cultivate effective emotion regulation skills, resulting in emotional dysregulation and behavioral issues. When confronted with interpersonal conflicts or negative emotions, they were unable to effectively identify, express, and regulate their emotions, leading to emotional build-up and loss of control. Before the crime, the suspect had a good relationship with the victim on the surface, but there might be hidden undetected conflicts or jealousy, such as envy of the victim's family conditions. The unresolved negative emotions were inadequately controlled throughout time, resulting in their steady accumulation until they attained a critical threshold. This resulted in the individual losing emotional control and resorting to excessive violent acts to express his internal turmoil and wrath. In addition, due to the long-term lack of parental supervision and guidance, left-behind children lacked a clear understanding of the consequences of their behaviour. They were easily influenced by peer pressure or undesirable external factors. Under such circumstances, the three suspects may have failed to fully realise how serious the consequences of their actions would be, ultimately leading to the tragedy.

3.2. Lu DaoSen's Suicide

Chinese photographer Lu Daosen (Zhou Peng) committed suicide after posting a suicide note on social media in November 2021. Lu Daosen detailed his long-term psychological hardship as a left-behind child, including familial neglect, domestic violence, and school bullying, as well as his loneliness and helplessness as an adult, in his suicide note. Many individuals sympathized with his suicide message and called for social attention to left-behind children's psychological health, school violence, and domestic abuse.

According to attachment theory, Lu Daosen's feelings of loneliness and helplessness in adulthood can be attributed to his unstable attachment experiences throughout childhood. As a left-behind child, Lu Daosen lacked a stable emotional connection with his parents while growing up. In his suicide note, he mentioned that he wrote down his thoughts about his parents on paper and showed them, but they were just cast aside, which can be seen as his parents showing emotional neglect towards him and his desire for a good parent-child relationship. Attachment patterns established with parents are the root of an individual's future emotional health and social adjustment. Insecure attachment relationships lead to Lu Daosen's lack of emotional security and sense of belonging, which also makes it difficult for him to establish stable interpersonal relationships in adulthood and makes him prone to loneliness and helplessness. In addition, his emotional isolation was further exacerbated by domestic violence and school bullying during childhood, which made him lack trust in the outside world and made it difficult for him to seek or accept support from others.

Emotional dysregulation significantly contributed to Lu Daosen's suicide. According to emotion regulation theory, as a left-behind child, he experienced emotional deficits and isolation, compounded by inadequate parental support. This lack of guidance hindered his emotional regulation skills, impairing his ability to cope with negative emotions. His psychological trauma was intensified by childhood domestic violence and bullying, leading to a prolonged accumulation of unaddressed negative emotions. In adulthood, economic struggles and the isolation of freelancing reactivated his childhood trauma. Lacking effective emotion regulation strategies, he could not manage these complex emotions, resulting in a detrimental cycle of dysregulation that culminated in his tragic decision to end his life.

4. Recommendations

4.1. National Policy

Research has shown that parents accompanying their children as much as possible can significantly reduce the likelihood of children's undesirable behaviours [14], so increasing the amount of time parents spend with their children is the key to solving the psychological problems of left-behind children. The reason why left-behind children in rural areas lack parental accompaniment is that the rural economic income is low, and parents need to go out to work to increase the family's economic resources. Thus, the state should support rural industries and modernize agriculture and rural characteristic industries through policy support, technology introduction, and capital investment to boost rural economies. To create more local jobs for rural adults, rural tourism, e-commerce, and handicrafts should be developed. When adults can obtain a stable income and room for development right in their hometowns, they will no longer need to go out to work, which will radically reduce the number of left-behind children. Parents will be able to accompany their children, giving them emotional support and nurturing care and avoiding the problem of emotional neglect caused by prolonged separation. This helps to promote the mental health development of left-behind children and reduce the incidence of their emotional disorders and behavioural problems.

In addition, to effectively address the problem of left-behind children’s lack of affection, the state can introduce special policies, such as the implementation of the ‘child companion mother’program. Through the selection and training of professionals with backgrounds in psychology and education, each‘child companion mother’ is responsible for the left-behind children in a village and regularly visits, accompanies, and cares for them, providing emotional support and psychological counselling. The government should create special funding to cover the salaries and training of "child companion mothers" and monitor and evaluate the program to ensure its efficacy. It should also inspire social forces to construct a government-led, socially coordinated care system to improve left-behind children's mental health and socio-emotional development.

4.2. School Education

To promote the healthy psychological development of left-behind children, schools should also adopt multi-level and systematic interventions. Firstly, schools should carry out regular class meetings on mental health education and incorporate the contents of emotion management, stress coping, and interpersonal communication into the curriculum system to help left-behind children master basic psychological adjustment skills [15]. Secondly, schools need to establish a mental health screening mechanism to regularly assess the psychological status of left-behind children through professional psychological assessment tools, identify potential problems in time, and provide personalised counselling. In addition, schools should strengthen family education guidance, popularise mental health knowledge to guardians of left-behind children through parent schools, online lectures, etc., and improve their emotional support and parenting skills. Schools should establish psychological counseling rooms staffed by professionals to offer individualized support for left-behind children. Additionally, implementing peer support programs can foster social belonging and emotional connections through group activities. These comprehensive strategies can significantly enhance the psychological well-being of left-behind children and support their overall development.

5. Conclusion

The mental health problem of left-behind children is a complex social phenomenon, which involves various factors such as family, school, and society. In this paper, the causes of left-behind children's psychological and behavioural problems are discussed in depth through parenting care theory, attachment theory, emotion regulation theory, and psychological capital theory, and targeted intervention suggestions are put forward in conjunction with actual cases. However, the solution to the problem of left-behind children requires not only theoretical support but also concerted efforts from all sectors of society.

Future research should enhance long-term tracking of the psychological health of left-behind children, examining developmental trajectories across regions and ages, along with their influencing factors. Additionally, interdisciplinary collaboration is essential, integrating theories and practical insights from psychology, education, and sociology to develop a systematic and personalized intervention model In addition, with the development of science and technology, digital intervention means, such as online psychological counselling, are also expected to provide more convenient and efficient support for left-behind children. It is hoped that in the future, through policy support, social care, and individual efforts, the psychological development gap between left-behind children and non-left-behind children can be gradually narrowed, creating a healthy and loving environment for every child to grow up in and contributing to the harmonious and sustainable development of society.