Parental absence is greatly associated with school bullying victimization of LBC in migrant families. As noted, LBC were at significantly higher risks of school bullying victimization compared with their counterparts who have never been left-behind (17). Zhang et al. found that above 30% of LBC reported being recurrently bullied (18). Additionally, being left-behind by migrant parents may further exaggerate the effects of bullying victimization on life satisfaction among children and adolescents (19). However, newly emerging forms of bullying victimization other than school bullying victimization, for instance, cyberbullying victimization among LBC, is yet to explore.

Bronfenbrenner's ecological systems theory (20) underscores the family as the most influential microsystem in child development. Extensive research yields compelling evidence for the critical role of parents in children's experiences of cyberbullying victimization. On one hand, parents influence children's susceptibility to cyberbullying through their parenting practice and oversight. For instance, a study involving Romanian adolescents demonstrated that a supportive parenting style serves as a protective factor, shielding adolescents from cyberbullying victimization (21). Similarly, Wu et al. found that parental rejection from both fathers and mothers increases children's risk of experiencing cyberbullying, slowing down the decline in such victimization over time (22). Parental neglect also amplifies the risk of children being exposed to cyberbullying (23). On the other hand, the quality of parent-child relationship is a key predictor of children's vulnerability to cyberbullying. Adolescents who have a more positive and satisfying relationship with their parents are less likely to experience cyberbullying (21, 24). Liu and Chen found that parent-child closeness plays a crucial role in reducing the risk of adolescents being victims in cyberbullying (25). As primary actors in family function, effective parent-child communication also serves as an essential protector of LBC's cyberbullying victimization (10, 26). Parent-child communication enhances adolescents' social skills, such as adequate coping and social support networks (27). However, due to parental migration, the form and quality of parent-child communication changed because of the broken family structure for LBC (28, 29). Despite these findings, studies examining the effects of parent-child communication on the association between parental migration and children's cyberbullying victimization remain scarce in China.

Self-determination theory (30–32) has been widely used to explain individual's intrinsic motivation for internet usage. According to this theory, individuals possess three fundamental psychological needs: autonomy, competence, and relatedness. The need for relatedness specifically refers to the longing for connection with others—to love and care for others, as well as to be loved and cared for in return. For LBC who are unable to live with their parents, a lack of intimate parent-child interaction might drive children to continually check messages on their Internet-connected devices (33) and to interact with others through social networking sites (34), potentially increasing their vulnerability to cyberbullying due to extended time spent online. Routine activity theory offers valuable insights for understanding diverse patterns of individual victimization (35). When children have more opportunities to access the internet, i.e., availability, their likelihood of experiencing cyberbullying also increases. Previous literature has highlighted that children who spent more time online were more likely to experience cyberbullying (36). One study conducted in Vietnam revealed the dose-response association between the average daily time spent on the Internet and the risk of experiencing cyberbullying (37). Furthermore, capable guardians play a pivotal role in influencing children's vulnerability to cyberbullying. Legate et al. found that cyberbullying can be reduced if parents discipline children by restricting their Internet access (38). Likewise, Sasson and Mesch reported that the restrictive measures taken by parents would prominently reduce the risks of cyberbullying victimization among children (39). In China, LBC tend to live with their grandparents or other relatives, especially those with both parents migrating (40), which leads to weakened parental supervision (41, 42). It is reasonable to infer that LBC may be more vulnerable to becoming victims of cyberbullying due to their increased time spent online.

Positive parent-child communication plays a crucial role in fulfilling children's psychological needs, consequently reducing their dependence on electronic devices. Conversely, inadequate parent-child communication can lead to an increased time spent online among children. According to the compensatory satisfaction theory of pathological internet use (43), if children experienced low levels of psychological need satisfaction in real life, they may turn to excessive internet use. Multi-family group therapy aimed at addressing internet addiction in adolescent has shown substantial reductions in internet usage time by enhancing parent-child communication (44). Moreover, the style of parental mediation significantly influences adolescents' exposure to cyberbullying victimization on social media (45). Parents can actively manage their adolescents' online activities using strategies such as co-use or restriction (46). Additionally, parental monitoring of children's activities can bolster the cultivation of their self-control and prosocial behavior, thereby reducing the likelihood of involvement in cyberbullying victimization (47).

Based on the aforementioned literature, we may infer that a combination of worsened parent-child communication and lengthened children's time spent online may put LBC at a greater risk of cyberbullying victimization; however, this topic is seldom explored in China. Therefore, the current study focused on currently left-behind children (CLBC) and previously left-behind children (PLBC) and advanced the knowledge. Four hypotheses were proposed.

H1: Current left-behind status or previous left-behind experience positively associated with cyberbullying victimization among children.

H2: Parent-child communication mediates the relationship between current left-behind status or previous left-behind experience and cyberbullying victimization among children.

H3: Time spent online mediates the relationship between current left-behind status or previous left-behind experience and cyberbullying victimization among children.

H4: Parent-child communication and time spent online serially mediate the relationship between current left-behind status or previous left-behind experience and cyberbullying victimization among children.

Figure 1 shows the hypothesized research model of the present study.

This was a cross-sectional questionnaire-based survey conducted in Anhui and Zhejiang province, China, from November to December 2020. Anhui Province is one of the provinces in which the number of LBC exceeds two million (2). Although Zhejiang is a national economy developed province, there is a large proportion of LBC in Kaihua County. A school-based multistage sampling method was employed to select the study population. First, three townships from a total of eight rural townships within Nanling County and three townships from a total of nine rural townships within Kaihua County were selected. Then, a primary school, and a junior high school with the highest proportions of LBC students were selected from a complete list of all schools in each township. To be eligible for this study, students need to be in Grade 5–8 (mostly including children aged 10–14) from the selected schools, and 1–4 classes were randomly selected from each school. Details of this survey were described in our previous paper (48). There were twelve schools enrolled in the present study (six primary schools and six middle schools). Of 3,025 eligible students, 2,931 completed the questionnaire, representing a response rate of 96.7%. Among these, 486 students were excluded for not meeting inclusion criteria (i.e., either parent of the child was divorced, remarried, or deceased); 90 questionnaires were identified as invalid for lack of key information about parental migration trajectories; 394 students were excluded for never accessing the Internet. Therefore, 1,961 questionnaires were included for the final analysis.

Chi-squared (χ²) tests and one-way analysis of variance (ANOVA) were employed to compare sample characteristics among CLBC, PLBC, and NLBC including social-demographic characteristics, parental migration status, cyberbullying victimization, parent-child communication, and time spent online. All analyses were performed using SPSS 25.0 and assumed a statistical significance level of p < 0.05.

We performed confirmatory factor analyses to evaluate the structural validity of the scale for the variables. To explore the mediating effects of parent-child communication and time spent online, we conducted path analysis using the maximum likelihood method. We performed 2,000 bootstraps and determined the presence of a mediating effect based on whether the confidence intervals included zero (54). The hypothesized integrated model was tested using Mplus 8.3.

Among 1,961 participants, 792 (40.4%) were CLBC, 541 (27.6%) were PLBC, and 628 (32.0%) were NLBC. Descriptive statistics for the measurements are presented in Table 1. Males (53.1%) slightly outnumbered females (46.9%), and there were more students in middle school (57.1%) than in primary school (42.9%). More than two-thirds of students had siblings (71.4%). The majority of students came from families with fair (66.9%) or wealthy (25.5%) economic status. More than 80% of students reported their fathers' education level to be middle school or above, and more than 70% of students reported their mothers' education to be middle school or above.

The prevalence of cyberbullying victimization in nine forms is shown in Table 2. Overall, 27.4% of students reported cyberbullying victimization during this semester. Being posted mean or hurtful comments online was the most common form of cyberbullying victimization (13.7%), followed by being excluded from online communication or games on purpose (9.6%).

Table 3 shows mother-child communication, father-child communication, time spent online on weekdays and weekends, and the prevalence of cyberbullying victimization among CLBC, PLBC, and NLBC, respectively. CLBC reported lower scores on mother-child communication (58.25 ± 15.20 vs. 60.49 ± 14.90) and father-child communication (61.08 ± 15.32 vs. 62.56 ± 15.83) than NLBC. And PLBC reported lower scores on mother-child communication (57.49 ± 15.55 vs. 60.49 ± 14.90) and father-child communication (58.94 ± 16.27 vs. 62.56 ± 15.83) than NLBC. Compared with NLBC, CLBC and PLBC spent more time online on both weekdays and weekends. The prevalence of cyberbullying victimization was higher among CLBC (29.3%) and PLBC (29.2%) than NLBC (23.4%).

Then, the integrative model was examined. The path analysis revealed that the current left-behind status was associated with higher prevalence of cyberbullying victimization among children (β = 0.076, p = 0.024), while the previous experience of being left-behind did not demonstrate a statistically significant correlation (β = 0.058, p = 0.087). Regarding the examination of mediating effects, the current status of being left-behind was associated with worse parent-child communication, which, in turn, predicted a higher prevalence of cyberbullying victimization among children [β = 0.019, 95% CI = (0.007, 0.036)]. Likewise, the previous experience of left-behind was associated with worse parent-child communication, which, in turn, predicted a higher prevalence of cyberbullying victimization [β = 0.026, 95% CI = (0.013, 0.043)]. Moreover, the current left-behind status was associated with increased time spent online, which, in turn predicted a higher prevalence of cyberbullying victimization among children [β = 0.024, 95% CI = (0.013, 0.038)]. However, no independent mediating effect of time spent online was observed between previous left-behind experience and cyberbullying victimization [β = 0.006, 95% CI = (−0.004, 0.016)]. Additionally, the current left-behind status positively predicted cyberbullying victimization among children through the serial mediating roles of parent-child communication and time spent online [β = 0.003, 95% CI = (0.001, 0.006)]. Similarly, previous left-behind experience positively predicted cyberbullying victimization among children through the serial mediating roles of parent-child communication and time spent online [β = 0.004, 95% CI = (0.002, 0.007)]. The standardized coefficients are presented in Figure 2 and Table 4.

The current study explored the influence of parental migration on child cyberbullying victimization, and potential mechanisms. Four major findings were generated from our analyses: first, the current status of being left-behind increases the risk of experiencing cyberbullying among children. Second, parent-child communication can mediate the association between current status or previous experiences of being left-behind and cyberbullying victimization among children. Third, the current left-behind status is linked to time spent online, which, in turn, positively correlates with cyberbullying victimization among children. Fourth, parent-child communication and time spent online play serial mediating roles in the association between the current status or previous experiences of being left behind and cyberbullying victimization among children.

The current left-behind status is associated with a higher prevalence of cyberbullying victimization, making CLBC a group that requires particular attention in preventing cyberbullying victimization. In contrast to PLBC, who have already reunited with their migrant parents, CLBC confront the absence of their parents. Face-to-face parent-child interaction is dramatically decreased with the long parent-child separation, and the parent-child communication of LBC is inevitably affected (4, 55). As noted, parents are important channels for children to acquire appropriate Internet knowledge or skills. Good parent-child communication can protect children from cyberbullying victimization (10, 56) by guiding their media use to reduce their susceptibility to engaging in risky activities (57). Impaired parents-child communication can also put LBC in a disadvantaged situation. Migrant parents may have to adopt a lighter touch on LBC's Internet usage because of the time-space span resulting from parent-child separation (58). Without proper parental supervision and monitoring, CLBC were more likely to become addicted Internet users than their counterparts because of longer time spent online (53), and they are more likely to experience cyberbullying (59, 60). Furthermore, for CLBC, functioning as a communication bridge between migrant parents and them, the Internet has already integrated into their daily life, and their time spent online is naturally longer than NLBC, which further urges proper parental supervision and monitoring.

For children who were previously left-behind and are now living with their parents again, parents can actively manage their children's internet usage. Nonetheless, parent-child communication still acts as a mediator between previous left-behind experience and increased risk of cyberbullying victimization among children. This may be attributed to the enduring impact of the parent-child separation on parent-child communication even after children reunite with their parents, as immediate improvement may not occur. This challenge may arise from parents facing their children's altered feelings and emotional needs compared to before the separation (61). Previous research similarly suggests that the previous left-behind experience affects the parent-child communication after reunification, thereby increasing mental health risks among children (62). Moreover, poor parent-child communication increases the likelihood that LBC will rely on the internet for psychological fulfillment. As a result, spending more time online will further increase their susceptibility to cyberbullying.

Our study extends the application of ecological systems theory to investigate cyberbullying victimization among children within the context of parental migration. As a crucial environment factor in children's development, the current separation of children from their migrant parents can influence parent-child communication, thereby increasing the risk of children becoming victims of cyberbullying. Importantly, the disruptive nature of intra-family communication persists even after migrant parents are reunited with their children. The lasting impairment of parent-child communication leads children to desire more online interaction, consequently elevating their risk of victimization.

Based on our findings, we propose several implications for intervention targeting cyberbullying victimization among LBC. Parent-child communication appears to be an essential for protecting both CLBC and PLBC from cyberbullying victimization. For children currently left-behind, migrant parents can use mediated and other long-distance communication devices to engage in communication with their children. These long-distance communication can help bridge the spatial gap between family members (63, 64), as indicated by the compensation theory (65). Research has demonstrated that migrant parents can establish positive communication with their children through tools such as video calls (66). Smart-phones offer new spaces for LBC, which can serve as an important supplement to emotion socialization of them (67). Parents often prioritize LBC's academic performance over concerning their emotional needs during telephone conversations (68). Therefore, when leveraging information and communication technologies to enhance frequency of interaction, it is prime for migrant parents to make an effort to address their children's psychological needs. Additionally, for CLBC, due to the absence of parents, managing their digital device usage is crucial. Reducing their internet usage time can help lower the risk of cyberbullying victimization. It might be a good option for migrating parents to turn their children's mobile phones into the Youth Mode (a settable mode that can effectively help parents manage the time of children's Internet access) regardless of the time-space span resulting from parent-child separation. For CLBC whose both parents are absent, caregivers should acquire knowledge of Internet usage to assist children in accessing the internet appropriately. In rural China, there is a scarcity of entertainment facilities, and children have relatively few playmates. As a result, children without their parents present rely on smartphones for entertainment (67). It is essential for the government to implement measures to enhance recreational activities in rural areas, offering more opportunities for children to engage in activities beyond the digital entertainment. For children who were once left behind, it is more important to take effective measures to strengthen parent-child communication upon their parents' return, reshape the parent-child relationship, in order to reduce the risk of children being victims of cyberbullying. To establish intimate parent-child communication, migrated parents can take relevant courses such as parent effectiveness training to polish their parent-child communication skills (69).

Recently, the Chinese government revised the Law on Protection of Minors and introduced a new chapter on online protection to safeguard the rights of minors in cyberspace. It proposed measures to enhance the promotion and education of minors' digital literacy across the national, social, school, and family levels. At the family level, it is proposed that parents or other guardians of minors should regulate their own behavior of accessing the Internet and reasonably arrange the time spent online of minors. The current study emphasizes that parents can mitigate the risk of cyberbullying victimization among children by strengthening parent-child communication. Particularly, tailored measures need to be taken to promote the development of children in response to the differing circumstances of parental absence, both current and previous.

Several limitations should be mentioned. First, the cross-sectional design can only examine associations rather than causal relationships. Subsequent studies applying longitudinal design to validate these associations would be especially meaningful. Second, we did not consider whether the LBC were left behind by both parents or just one, as well as their living with grandparents. Future research should take these factors into account to gain a more comprehensive understanding and clarify the relationship between parental migration and child cyberbullying victimization. Third, the key variables in the current study were based on students' self-reports, which may introduce reporting bias. However, one previous study noted that no difference in effect size was addressed between studies using only self-reports and those using other reports and self-reports simultaneously (14). Fourth, the study sample was limited to children in two provinces of China, which may affect the generalizability of our findings, especially the prevalence of cyberbullying victimization among children. Fifth, the children's time spent online measured in this study did not distinguish academic usage from entertainment usage.