Introduction

Left-behind children are children under 16 years old who have been left behind in their rural hometowns when their parents migrate elsewhere to work [1]. Parental labor migration is common in some developing countries (China, South and South East Asia, and Africa), causing many children to be left behind [2, 3]. Henan is a large province of left-behind children; as of 2021, 1,595,600 rural left-behind children in compulsory education are in school, accounting for 10.70% of the total number of students in compulsory education, excluding preschool left-behind children (More than 120,000) [4]. In 2016, the government promulgated the “Opinions on Strengthening the Care and Protection of Children Left Behind in Rural Areas,” The “Opinions” require a sound mechanism and strengthened supervision to solve the problem of children left behind by 2022. Building a management system and education for left-behind children is an important task.

Preschool left-behind children mean left-behind children in preschool education from 3 to 6 years old. This period is the essential stage of children’s motor skills acquisition and the best time to become proficient in stability, mobility, and movement skills [5]. At this time, if the foundation of motor skills is laid, developing body movement habits can bring lifelong benefits [6, 7]. During the 3–6 years of age, children’s gross motor movement reaches a primary stage where children’s coordination and level of motor control are improved to some extent [8, 9]. If children are given enough motor skill practice and instruction at this time, they can develop early motor experiences and promote the development of gross motor movement. The 3–6 year old stage is critical for essential motor development [10]. Gross motor movements are the basis for later high motor and special motor skills. They are an essential way to explore the environment later and learn about the world around them. If children do not acquire the correct basic movement patterns early in life, their ability to acquire different combinations of gross motor movement will be significantly reduced [11, 12]. Therefore, optimal development of these skills is essential for the developing child.

The development of gross motor movement in early childhood mainly includes the separate locomotor and the action behavior of manipulating objects, which is an integral part of fundamental motor skills [13]. Separate locomotor mainly refers to the movement of the body in space, including running, jumping, crossing, sliding, fast and sharp stopping, etc. 3–6 years old is the peak and sensitive period of movement development, and many gross motor movement development changes a lot before the age of 8 [14]. Therefore, focusing on the development of gross motor movements such as walking, running, jumping, and throwing from the early childhood stage is very important for the mastery of advanced motor skills in the future. Furthermore, research has shown that gross motor movement enables children to achieve their goals of independent activity and exploration, which benefits their physical and mental health and social adaptability. Studies have confirmed that gross movement is closely related to physical health and cognitive development [15–17]. Motor development is essential for monitoring, evaluating, and diagnosing individuals’ physical and mental development [18]. Gross motor movements can predict physical activity participation, physical fitness levels, and even cognitive performance in adulthood [19].

Motor development theory suggests that gross motor movement is stage-specific and programmatic as one of the critical components of movement development [20]. From infancy to adolescence, gross motor development increases with age [21]. However, it has been shown that many children need to obtain mastery levels of competency in many gross motor skill test items, especially object control and ball handling skills such as throwing, catching, and striking [22]. This affects their performance in athletic endeavors, but more importantly, it may affect their affinity for moderate-to-vigorous physical activity [23]. Therefore, intervention and training of fundamental movement skills at 3 to 6 years old can facilitate children to reach a higher level of movement in their future daily lives. Therefore, it is vital to grasp the golden period of children’s learning to do systematic and efficient movement, play, and learning.

The Internet plays an increasingly important role in the development of children and adolescents [24]. While optimizing children’s learning and lives, the Internet has also brought about social problems [25]. Among such social problems, Internet addiction or screen time has received considerable attention [26, 27]. The use of Internet media can harm all aspects of children’s body functions: It causes eye fatigue and reduces vision levels; Prolonged video screen time will put children in a "sedentary" state, squeezing out time for outdoor activities, quickly leading to obesity and a lack of motor skills; Using electronic products so that children are often crouching or lying on the bed or sofa affects children’s cervical vertebrae and lumbar vertebrae, causing harm, which affects growth and development [28, 29].

Children’s use of electronic devices is becoming increasingly popular, and children’s poor self-control during this period may lead to electronic addiction if they are overexposed [30]. Related studies have also found that left-behind children spend more time on screens than the average child [31]. Although many people call for parents to return to their families to solve the problem of Internet addiction among left-behind youth, many parents are forced to work outside the home to make ends meet, and this situation is quite helpless but burdensome to change [32]. Cognitive characteristics and parenting patterns are more accessible to change than those of the left-behind situation [33]. Therefore, guardians play a vital role in preschool left-behind children’s screen time. Guardians can also take measures to monitor, manage, and educate children’s media use behavior in their daily lives to help children use media reasonably and correctly [34].

Studies have shown a correlation between visual screen time, physical activity, and motor skills in children [35]. Unreasonable screen time for children and adolescents will hurt their physical and mental health, such as poor vision, obesity, sleep disorders, anxiety, Internet addiction, decreased physical activity, and impaired language development [36, 37]. Physical activity levels are reported to be low in preschool children [38, 39]. Generally, preschool children engage in high amounts of sedentary behavior and low physical activity. The rise in preschoolers’ screen time impacts their physical activity. Studies have shown that the level of gross motor movement in preschool children is directly related to physical activity [40]. However, the importance of gross motor movement is often overlooked by guardians who generally need more knowledge about parenting related to children’s need for extensive physical activity. Based on the existing literature, the following hypotheses were proposed: There is a negative correlation between screen time and gross motor movement levels among preschool left-behind children.

Therefore, this study investigated the current screen time and gross motor movement of left-behind children aged 3–6 and identified the correlation between both. This study is intended to provide a theoretical basis for guardians to address the importance of gross motor movement in left-behind children.

Methods

Results

Screen time (>2h/d) of left-behind children aged 3 to 6 years old by gender

As shown in Table 1, the average daily screen time of left-behind children aged 3–6 years increased gradually with age during one week, and the difference in the detection rate of >2h/d screen time was statistically significant (p < 0.05). The difference in the detection rate of >2h/d screen time of left-behind children aged 3–6 years was also statistically significant (p < 0.05) for different genders, respectively.

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Table 1. Average daily video screen time for 1 week for left-behind children aged 3 to 6 years.

https://doi.org/10.1371/journal.pone.0296862.t001

Gross motor development characteristics of left-behind children aged 3 to 6 years

As shown in Table 2, the total gross motor movement score, separate locomotor score, and ball skill score of children aged 3 to 6 increased significantly with age, and the differences were statistically significant (F = 10.782, 5.293, and 7.688; P<0.01).

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Table 2. Gross motor movement characteristics of left-behind children aged 3 to 6 years.

https://doi.org/10.1371/journal.pone.0296862.t002

Analysis of the correlation between gross motor development and screen time in left-behind children aged 3 to 6 years

As shown in Table 3, there were significant negative correlations between total gross motor movement scores, separate locomotor scores, ball skill scores, and screen time for the left-behind children in each age group from 3 to 6 years old (P<0.05).

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Table 3. Analysis of the correlation between gross motor movement and screen time among left-behind children aged 3 to 6 years.

https://doi.org/10.1371/journal.pone.0296862.t003

Given the significant correlation between gross motor movement and screen time in left-behind children aged 3–6 years, further investigate the effect of screen time on gross motor movement. This study used screen time as the dependent variable, age, and gender as independent variables in the first model, and gross movement total score in the second model for multiple linear regression analysis. As shown in Table 4 The total screen time score was predictive of the gross motor movement total score (adjusted R² = 0.184, p<0.001), with an explanatory rate of 21.4%. Specifically, for every 1-unit change in the total screen time score, the total gross motor movement score changes by -0.689 standard deviations.

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Table 4. Multiple regression analysis of screen time and gross motor movement among left-behind children aged 3 to 6 years.

https://doi.org/10.1371/journal.pone.0296862.t004

Discussion

With China’s economic and social development, many rural parents go out to work. They leave their children behind in their hometowns and entrust their children to their elderly grandparents to raise. As a result, a large group of left-behind children has been formed in China. For a long time, the government and society have focused on caring for left-behind children to ensure they are well-fed and well-clothed. With smartphones and mobile Internet popularity in rural areas, increased screen time is becoming a new problem. It is urgent to implement "source management" by the supervisory department. At the same time, the cooperation of schools, families, and society is needed to create a safe and healthy space for left-behind children to grow up. The left-behind children were chosen for this study because the lack of parental roles significantly impacts the environment in which left-behind children grow up, making this population a particular risk group for early childhood development.

Studies have shown that the lack of family management is the main reason for increased screen time for left-behind children [50]. Guardians of left-behind children cannot restrain left-behind children from using cell phones, tablets, or watching TV. Guardians need to do housework or other tasks while looking after children, making it challenging to keep an eye on them throughout the day. Guardians use cell phones and tablets as "babysitters" so the children do not run around and disturb themselves. As a result, left-behind children have the power to dominate their phones or tablets too early and become attached to the online world from an early age.

On the other hand, some studies have confirmed that the decline in children’s physical fitness is closely related to physical inactivity [51]. Physical inactivity among children has become a global universal problem, especially among children left behind in rural than urban areas [52]. Related research confirms that children with higher screen time spend less time engaged in TPA (Total of Physical Activity), MVPA (Moderate-to-Vigorous Physical Activity), and VPA, and more time in static behavior (chiefly screen-time behavior) [53]. Reducing static behavior and increasing physical activity has become a common demand for public health and physical education efforts. Regular physical activity can have several health-promoting effects on preschoolers, including promoting growth and enhancing gross motor movement levels [54, 55]. Therefore, this study was conducted to investigate whether there was a correlation between screen time and gross motor movement in left-behind children aged 3 to 6 years old and to analyze the differences in the characteristics of screen time and gross motor movement in left-behind children aged 3 to 6 years old.

This study showed that the development of locomotor ability, ball skill ability, and gross motor movement of left-behind children in each age group differed significantly with age and showed an overall increasing trend, which was consistent with the results of other prior studies [56]. It has been shown that children aged 3–6 are at a critical time in developing motor skills [57]. Suppose they are not given adequate stimulation during this period. In that case, it will affect the learning of motor skills and the physical application of complex movements later in life [58]. Therefore, in the motor learning of 3-6-year-olds, emphasis can be placed on learning through gross motor movement and exploring their surroundings to learn motor skills. Fundamental motor skills and various basic motor skills must be developed during preschool.

This study found that the average daily screen time increased with age among left-behind children aged 3–6 years, with significant differences between ages, and the reported rates of >2 h/d ranged from 22.43% to 33.73%. Cyberspace fits with curiosity and children’s nature of liking games, being spontaneous, unrestrained, and chasing pleasure. Children need to judge the Internet correctly; they are only interested in sound and images, so games and animation become their only knowledge of cell phones, computers, and the Internet. The amount of screen time for children aged 3 to 6 years is related to the child’s age; usually, the older the preschooler, the longer the screen time. Studies have shown that too few restrictions on children’s video screen content can hurt children’s play, hobbies, sleep hygiene, and eating habits [59].

Most guardians were unaware of unhealthy viewing and the associated deleterious effects. Past studies have shown that excessive screen time can lead to poor posture, scoliosis, impairment of motor coordination, visual perceptual development, cognitive brain development, poor concentration and creativity, behavioral deviations, and physical health, affecting many children with poor physical fitness [60]. Although excessive screen time has some negative impacts on children, as children grow, a one-size-fits-all approach is not advisable [61]. Guardians must decide how much media to let children use daily and what is appropriate. Establish clear rules and set reasonable limits for child’s use of digital media [62]. For example, for children ages 3 to 6, limit screen time to one hour a day of high-quality programming (videos that are beneficial to children’s development, such as educational videos, enlightenment videos, children’s dance videos, and children’s song videos). Guardians will likely need to continue to guide, manage, and monitor a child’s use of screens and media as he or she grows.

The present study showed that age was a significant predictor of gross motor development in children aged 3–6 under multivariate analysis, and screen time was a predictor of gross motor movement level in children aged 3–6. This is because the development of the movement in the preschool years is almost simultaneous with physical, emotional, and cognitive development. Significantly, the younger the age, the closer the relationship [63, 64]. Lack of experience with multiple basic motor skills in children 3–6 will negatively affect their later learning of fine or higher-level motor skills or cause difficulties in subject learning [65]. Therefore, motor development is not only related to the individual’s physical and mental growth and development but also to the individual’s future performance in learning and social interaction. In recent years, studies have found that children aged 3–6 lack time for physical activity, and 3C electronic devices such as TVs and cell phones limit children’s opportunities for physical activity, leaving children at a critical stage of their development with a dilemma in learning and motor development [66, 67]. The increase in screen time has led to more static activities and a decrease in physical activity with age, which is a situation that needs to be observed and improved.

The 2018 Guidelines for Exercise in Preschool Children were released, which state that it is essential to actively foster a lifestyle where exercise is part of children’s lives and stays with them throughout their lives between the ages of 3 and 6. The guidelines state that preschoolers should be active throughout the day to promote growth and development and that guardians should encourage children to play actively and should not exceed one hour of screen time. Therefore, it is recommended that guardians of left-behind children should limit children’s video screen behavior promptly and should be able to promote the health of children and adolescents with at least 60 minutes of moderate physical activity daily to enhance the level of gross movement of left-behind children aged 3 to 6 years [68].

Conclusion

There is a correlation between screen time and gross motor movement development in children aged 3–6 years old left behind, and the gross motor movement ability of children aged 3–6 years old can be developed by reducing screen time and increasing physical activity. This study can be used to inform teachers and families of the association between levels of screen time and the gross motor movement ability of children aged 3–6 years old. We suggest that guardian should guide and supervise children to reduce the screen time and encourage more verbal contact with the environment, to reduce damage to gross motor coordination.