Lifestyle behaviors from early childhood to junior high school in rural Japan: a cross-sectional study

Abstract

Background

Understanding combinations of lifestyle behaviors, including screen time, outdoor activity, and sleep, is essential for promoting children’s health. However, evidence spanning multiple developmental stages within the same community remains limited, particularly in rural areas of Japan.

Methods

This cross-sectional study examined school stage and sex differences in lifestyle behaviors among children living in a rural region of southern Japan. Participants included 1,192 children from early childhood through junior high school (49.8% girls, 50.2% boys), recruited from a total of 10 schools (four preschools, four elementary schools, and two junior high schools) in the study areas. In Japan, preschool includes children aged 1–5 years, elementary school includes Grades 1–6 (ages 6–12), followed by junior high school (Grades 7–9; ages 12–15) and high school (Grades 10–12; ages 15–18). Information on sleep timing, sleep duration, outdoor activity time, and screen time was collected using parent- and self-reported questionnaires. Differences by school stage and sex were analyzed using two-way analysis of variance and chi-square tests, with linear regression models used to examine trends across ordered developmental stages.

Results

Across all school stages, average sleep duration fell below age-specific recommendations, decreasing from 9.60 h/day in toddlers to 7.83 h/day in junior high students. This decline was driven by progressively later bedtimes (21:02 to 22:42) rather than changes in wake times. Screen time exhibited a nearly fourfold increase across stages, rising from 1.46 to 5.70 h/day (p < 0.001), suggesting early consolidation of screen-related behaviors. Outdoor play time was 0.28 h/day in toddlers, 0.38 h/day in preschoolers, 0.55 h/day in both lower and upper elementary school children, and 0.85 h/day in junior high school students.

Conclusions

Unhealthy lifestyle behaviors related to sleep, physical activity, and screen use were observed across multiple developmental stages within a single rural community. These patterns appear to emerge early in childhood and intensify with age, underscoring the importance of a life-course approach and the need for early, developmentally appropriate public health strategies to support healthier daily routines among children in rural regions.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s12889-026-27954-5.

Background

Children’s lifestyle behaviors including physical activity(PA), screen time(ST), and sleep play a fundamental role in shaping their physical and mental health [1, 2]. These behaviors imbalances have been associated with increased risks of obesity, reduced physical fitness, impaired cognitive development, and poorer overall well-being [3, 4]. In particular, excessive screen time and insufficient sleep have been identified as global public health concerns among children [5, 6]. In recent years, these lifestyle-related health challenges have been increasingly framed within a life-course public health perspective, emphasizing the importance of early behavioral patterns for later health trajectories [7].

National surveys have reported persistent declines in physical activity levels, increased sedentary behavior among school-aged children [8, 9]. In Japan, lifestyle-related health issues have become increasingly evident, especially among children living in rural areas [10]. In rural settings, children’s lifestyle behaviors may be influenced by environmental conditions, including limited opportunities for physical activity [11]. Previous studies suggest that children’s physical activity and screen time may vary depending on their living environment; however, findings regarding urban–rural differences remain inconsistent [12–14]. Moreover, most studies have been conducted in western countries, and evidence focusing on Japanese preschool-aged children remains limited. In Japan, one study highlighted the role of environmental factors, reporting that transportation convenience was negatively associated with outdoor playtime in rural areas, where children aged 11–12 years were more likely to rely on cars for daily mobility [15]. These contextual constraints may influence how lifestyle behaviors are formed, maintained, and altered across childhood. Furthermore previous research has examined specific lifestyle behaviors within certain age groups—such as preschoolers, elementary school students, or adolescents—studies rarely cover the full developmental spectrum [16, 17]. To date, very few studies have examined lifestyle behaviors continuously from early childhood through elementary school within a single community, even though habits established in early childhood often persist into adolescence and beyond [18]. From a public health standpoint, examining lifestyle behaviors across consecutive developmental stages within the same social and environmental context is critical. Such an approach allows for the identification of developmental windows during which unhealthy behavior patterns emerge or intensify, thereby informing the timing and targeting of preventive interventions. Understanding how lifestyle behaviors vary across school grades within the same rural community is therefore essential for designing effective, developmentally appropriate interventions. Given these gaps, the present study examines grade-level differences in lifestyle behaviors—such as sleep duration, outdoor playtime, and screen time—among children living in a rural area of southern Japan from early childhood through junior high school. By focusing on a single rural community and spanning multiple developmental stages, this study seeks to clarify when unhealthy lifestyle patterns first become evident and how they evolve across childhood. The findings are expected to contribute to improved life-course-oriented health education policies and community-based support strategies for children in rural Japan. The aim of this study was to examine developmental-stage differences in lifestyle behaviors. We hypothesize the following: (a) There are significant differences in ST, sleep duration, and outdoor play time among children aged 1–15 years, according to age group. We expect that screen time will be higher in the older group, while sleep time and outdoor play time will be higher in the younger group. (b) There are significant differences in outdoor play time among children aged 1–15 according to sex, with boys being more active than girls, but no significant differences in ST and sleep duration according to sex. (c) Children’s weekday behaviors related to ST, SL, and PA will deviate from the recommendations set forth by the UN.

Method

Participants

This cross-sectional study analyzed data collected from schools in rural areas (Sakawa Town) in Kochi Prefecture, Japan. Preschools, elementary schools, and junior high schools in these areas were invited to participate; ultimately, data were collected from four preschools, four elementary schools, and two junior high schools. Children’s lifestyle-related behaviors were assessed using a questionnaire administered between September and October 2021. The study was conducted in Kochi Prefecture, Japan (area: 7,103 km²; population: 669,516; population of children aged 0–14 years: 75,171) [19]. Kochi Prefecture is declining population and aging demographic structure. According to regional statistics, Kochi has a relatively smaller economic scale and lower average income levels compared to the national average, with a greater reliance on primary industries such as agriculture and fisheries [20]. This economic stagnation, coupled with a shrinking population, makes Kochi a representative model of rural Japan facing significant socio-economic challenges. Rural areas were defined based on the Densely Inhabited Districts (DIDs) classification provided by the Statistics Bureau of Japan. DID areas are defined as regions with a population density of at least 4,000 persons per km² and a population of 5,000 [21] or more. According to the DID boundary map from the 2020 Population Census [22], Sakawa Town were not classified as DID areas. Sakawa town had an estimated population of 12,306 in 6036 households and a population density of 120 persons per km². Per the Declaration of Helsinki, informed consent was obtained from the parents and teachers of children aged 1–15 years from the selected schools in Kochi, Japan. Data from 1,192 children (50.2% boys, 49.8% girls) whose parents or guardians provided written informed consent were included in the analysis. The questionnaire response rate was 74.6%.The study received prior approval from the Waseda University Ethics Committee, Faculty of Sports Science (2021-H043). Clinical trial number: not applicable.

Measurements

The questionnaire for younger children (1–8 years) was adapted from a Japanese-language preschool lifestyle behavior questionnaire [23]. The questionnaire for elementary and junior high school students (9–15 years) was adapted from a Japanese-language child lifestyle behavior questionnaire [24]. An English-translated version of the questionnaires is provided in Supplementary File 1 and File 2.

Bed time

Bedtime was assessed using the question, “What time does your subject child usually go to bed at night [23]? ” Parents provided this information for younger children. Elementary and junior high school students reported their own usual weekday bedtime; however, for elementary school students in Grade 3 or below, the questionnaire was completed with assistance from their parents or guardians.

Waking time

Waking time was assessed using the items “What time does your subject child usually wake up in the morning [23]? ”. Parents provided this information for younger children. Elementary and junior high school students reported their own usual weekday Waling time; however, for elementary school students in Grade 3 or below, the questionnaire was completed with assistance from their parents or guardians.

Sleep duration

The sleep duration was calculated by evaluating the reported bedtime and wake-up time [23].

Outdoor playtime

Outdoor playtime of preschoolers was assessed using the following item: “How much outdoor activity does your child indulge in on average after spending the day at the preschool on weekdays?” [23]. The parents were asked to freely enter the outdoor playtime on weekdays in the last week. For elementary and junior high school students reported their own usual weekday outdoor playtime; however, for elementary school students in Grade 3 or below, the questionnaire was completed with assistance from their parents or guardians.

Screen time

Screen time of preschoolers was assessed by asking parents how much time their children spent watching TV and using smartphones, tablets, and computers in the past week, using the following questions: (1) How many media devices, including TVs, smartphones, tablets, and computers, are available at home? (2) How much time does your child spend watching TV or videos in a day? and (3) For how long, on average, does your child use electronic devices, such as smartphones, tablets, and computers, in a day [23]? For elementary and junior high school students, the same questionnaire was used and completed by the students themselves; again, children in Grade 3 or below completed the questionnaires with the help of their parents/guardians. Average daily screen time was calculated by summing the reported time spent across three screen-based activities (e.g., watching TV/videos and using electronic devices such as smartphones, tablets, and computers).

Demographic variables

Participants’ gender and age were reported by parents or guardians for preschool children and self-reported by the participants for elementary and junior high school students. Height and weight were measured to the nearest 0.1 cm and 0.1 kg, respectively, with participants wearing light clothing and no shoes. Measurements were conducted by school nurses.

Statistical analyses

A two-way analysis of variance (ANOVA) was performed to examine the effects of sex and school stage on lifestyle variables, including outdoor time, screen time, sleep duration, bedtime, and wake-up time. School stage was categorized into five groups: Toddlers (1–2 years), Preschool (3–5 years), Elementary school lower (Grades 1–3), Elementary school upper (Grades 4–6), and Junior high school (Grades 7–9) [25]. When significant main effects or interactions were detected, Bonferroni-adjusted post hoc comparisons were conducted. Chi-square tests were used to compare proportions for categorical variables, including gender, age. In addition, to account for the ordinal nature of developmental stage/class grade, trend analyses were performed. For continuous outcomes (bedtime, wake time, sleep duration, outdoor time, and screen time), linear regression models were fitted with ordered school stage as the predictor and sex as a covariate. As an additional sensitivity analysis, linear regression models were also applied across school grades 1–9 among school-aged children only. All statistical analyses were conducted using IBM SPSS 25.0 [26], and the level of significance was set to p < 0.05.

Results

Participants’ characteristics

The characteristics of the children by sex are presented in Table 1. This study included 598 boys and 594 girls. The percentage of boys and girls was not significantly different in any school stage. No statistically significant sex differences were observed in height or weight.

Table 1.

Participants characteristics population

Variables	Boys	Girls	p-value
Number, n (%)	598 (50.2)	594 (49.8)
School stage, n (%)			0.58
Toddlers (1–2 years)	44(7.4)	46(7.7)
Preschool (3–5 years)	107 (17.9)	102 (17.2)
Grades 1–3	150 (25.1)	153 (25.8)
Grades 4–6	161 (26.9)	146 (24.6)
Grades 7–9	136 (22.7)	147 (24.7)
Body composition
Height, cm (mean ± SD)	131.0 (23.1)	129.0 (22.8)	0.24
Weight, kg (mean ± SD)	31.1 (14.4)	31.2 (14.5)	0.09

Data are presented as n (%) or mean ± SD unless otherwise stated. Categorical variables were assessed using chi-squared tests

P- value for Chi-square test

Bedtime

Figure 1A shows bedtime by school stage among preschoolers, elementary school children, and junior high school students. In both sexes, bedtime was progressively delayed with advancing school stage (p < 0.01). Among junior high school students, girls had significantly later bedtimes than boys (p < 0.01). Toddlers sleep earliest at 21:02, while junior high students stay up until 22:42 on average (β = 24.08, p < 0.001) Table 2.

Fig. 1.

Sleep behaviors across school stage in rural Japan. Note: (A)Bedtime, (B) wake time, and (C) sleep duration are shown by developmental stage and sex. Dark bars indicate boys and hatched bars indicate girls. Developmental stage was categorized as toddlers (1–2 years), preschoolers (3–5 years), E. school (G1–3; elementary school, lower grades, Grades 1–3), E. school (G4–6; elementary school, upper grades, Grades 4–6), and J.H. school (G7–9; junior high school, Grades 7–9). Values are presented as mean ± SD. **p < 0.01, ***p < 0.001

Table 2.

Lifestyle behaviors across developmental stage

Outcome	Toddlers (1–2 years) (n = 90)	Preschoolers (3–5 years) (n = 209)	Elementary school, lower grades (Grades 1–3) (n = 303)	Elementary school, upper grades (Grades 4–6) (n = 307)	Junior high school (Grades 7–9) (n = 283)	β for trend	p for trend
Bedtime, h	21:02 (00:33)	21:24 (00:36)	21:24 (00:38)	21:51 (00:48)	22:42 (00:41)	24.08	< 0.001
Wake time, h	06:38 (00:25)	06:43 (00:28)	06:28 (00:30)	06:28 (00:35)	06:35 (00:33)	-1.89	0.012
Sleep duration, h/day	9.60 (0.46)	9.31 (0.54)	9.05 (0.69)	8.60 (0.92)	7.83 (0.73)	-26.95	< 0.001
Outdoor play time, h/day	0.28 (0.61)	0.38 (0.81)	0.55 (0.92)	0.55 (0.92)	0.85 (1.27)	1.04	< 0.001
Screen time, h/day	1.46 (0.97)	1.75 (0.84)	2.89 (2.75)	4.82 (5.15)	5.70 (4.76)	76.02	< 0.001

Values are presented as mean ± SD. Bedtime and wake time are displayed as mean clock time (SD shown as HH: MM)

β and p for trend are from linear regression models using ordered developmental stage as the predictor and sex as a covariate

Waketime

Figure 1B shows wake times by school stage among preschoolers, elementary school children, and junior high school students. No significant sex differences were observed. However, significant differences were found across school stages: preschool children (3–5 years) woke later than elementary school students (Grades 1–3) in both boys and girls (p < 0.01). While wake times remain relatively stable (ranging between 06:28 and 06:43), there is a slight but statistically significant trend toward earlier waking in older groups (p = 0.012) Table 2.

Sleep duration

Figure 1C shows sleep duration by school stage. Significant sex differences were observed only among junior high school students. Sleep duration differed significantly across school stages. In both sexes, children aged 1–2 years had longer sleep duration than those aged 3–5 years (p < 0.01). Preschool children aged 3–5 years had longer sleep duration than elementary school students in Grades 1–3, and students in Grades 1–3 had longer sleep duration than those in Grades 4–6 (p < 0.01). Among junior high school students, girls had significantly shorter sleep duration than boys (p < 0.001). Sleep duration decreases drastically with age. Toddlers receive.6 h, which drops to 7.8 h by junior high school (β = -26.95, p < 0.001) Table 2.

Outdoor playtime

Figure 2A shows outdoor time by school stage. Significant sex differences were observed among elementary school students in Grades 4–6 (p < 0.05). Significant differences across school stages were also identified. Preschool girls aged 1–2 years spent less time outdoors than those aged 3–5 years (p < 0.05). Among boys, elementary school students in Grades 4–6 had shorter outdoor time than junior high school students (p < 0.05). Outdoor play time was 0.28 h/day in toddlers, 0.38 h/day in preschoolers, 0.55 h/day in both lower and upper elementary school children, and 0.85 h/day in junior high school students. Despite this late-stage dip, the overall trend remains positive ( β = 1.04, p < 0.001) Table 2.

Fig. 2.

Outdoor time and Screen time across school stage in rural Japan. Note: (A) Outdoor time and (B) screen time are shown by developmental stage and sex. Dark bars indicate boys and hatched bars indicate girls. Developmental stage was categorized as toddlers (1–2 years), preschoolers (3–5 years), E. school (G1–3; elementary school, lower grades, Grades 1–3), E. school (G4–6; elementary school, upper grades, Grades 4–6), and J.H. school (G7–9; junior high school, Grades 7–9). Values are presented as mean ± SD. *p < 0.05, **p < 0.01, ***p < 0.001

Figure 2B presents screen time by school stage. No significant sex differences were observed. However, significant differences were found across school stages. In both sexes, elementary school students in Grades 1–3 had significantly shorter screen time than those in Grades 4–6 (p < 0.01). Among girls, students in Grades 4–6 had significantly shorter screen time than junior high school students (p < 0.01).

Toddlers average 1.46 h/day, whereas junior high students average nearly four times that amount at 5.70 h/day ( β = 76.02, p < 0.001). The sharpest jump occurs between the lower and upper elementary school grades (increasing by over 1.92 h) Table 2.

Discussion

The present study examined age-related changes in sleep, physical activity, and screen time among children in a rural area of Japan. Overall, the findings revealed three main patterns. First, sleep duration decreased and bedtimes became progressively later with increasing school grade. Second, outdoor activity levels were consistently low, particularly during weekdays, and did not meet recommended levels across several age groups. Third, screen time increased markedly with age, with a particularly sharp rise observed from late childhood onward.

Sleep is a critical component of healthy development, particularly during the formative years from infancy through adolescence [27]. Regarding recommended sleep duration, the American Academy of Sleep Medicine suggests that children aged 1–2 years should sleep 11–14 h, those aged 3–5 years 10–14 h, children aged 6–12 years at least 9 h, and adolescents aged 13–18 years at least 8 h [25].In the present study, sleep duration from preschool through junior high school was consistently shorter than these recommended standards, indicating a tendency toward late bedtimes and short sleep duration. In Japan, widely accepted, age-specific quantitative guidelines for children’s sleep duration have historically been limited [28]; therefore, previous studies have commonly adopted international standards such as those of the American Academy of Sleep Medicine [29] or applied study-specific criteria [30]. The present study found that weekday sleep duration was relatively short across age groups, with averages of 9.0 h among preschool children, 8.6 h among elementary school children, and 7.8 h among junior high school children, all of which fall below the recommended sleep ranges. Compared with national data from Japan, these values are lower than the average sleep duration of approximately 8 h reported for children aged 10–14 years in the 2015 national survey [31]. Similarly, international evidence indicates somewhat longer sleep durations; for example, a large multinational study across 12 countries reported an average of approximately 8.8 h among children aged 9–11 years [32]. When compared with findings from urban populations in Spain [33], a similar pattern emerges. Although some children in these studies do not fully meet sleep recommendations, their average sleep duration generally remains close to the lower end of the recommended range. In contrast, the values observed in the present study suggest a greater degree of sleep insufficiency in this rural sample.

By sensitivity analyses restricted to Grades 1–9, which showed that advancing grade level was associated with later bedtimes, slightly later wake times, and shorter sleep duration. Notably, the delay in bedtime was substantially greater than that in wake time, suggesting that sleep loss is primarily driven by delayed sleep onset rather than compensatory changes in wake time. These results are consistent with previous research showing that sleep duration decreases with age across childhood and adolescence [34, 35]. This pattern is thought to be driven not only by biological changes, such as shifts in circadian rhythms, but also by social factors, including increasing academic demands and fixed school schedules [36, 37].From a life-course perspective, such early-emerging sleep patterns may have cumulative implications for later health and well-being [38, 39].

However, while these developmental patterns appear to be universal, the magnitude of sleep reduction observed in the present rural sample may be more pronounced. Previous research has indicated that the associations between sleep and lifestyle behaviors tend to be stronger in high-income countries, suggesting that social and environmental factors may intensify these patterns [32]. In this context, the rural environment in Kochi Prefecture may further shape children’s daily routines. Structural constraints such as school consolidation [40], limited access to extracurricular and recreational facilities may lead children to spend more time at home, longer commuting times, and limited access to recreational facilities may reduce opportunities for physical activity [19, 41] and increase reliance on screen-based activities, which in turn may delay bedtime and shorten sleep duration.

Taken together, these findings suggest that while age-related declines in sleep are a general developmental phenomenon observed across countries, the expression and magnitude of these changes may be influenced by local environmental conditions. In rural settings, these contextual factors may interact with biological maturation and social demands to further exacerbate sleep deprivation.

Sleep duration in this study was assessed based on parent- or self-reported data and was limited to typical weekdays. While weekday-based assessments are commonly used in school-based epidemiological studies due to their relative stability and comparability, they may not fully capture variations in sleep patterns across the entire week. In particular, children often exhibit different sleep behaviors on weekends, such as later bedtimes and longer sleep duration. Therefore, the findings should be interpreted as reflecting weekday sleep patterns rather than overall weekly sleep behavior.

Regarding physical activity time, the 2010 WHO guidelines recommend that children aged 5–17 years engage in at least 60 min of moderate- to vigorous-intensity physical activity daily, or perform vigorous-intensity activity on at least three days per week to promote muscle and bone development [41]. In the present study, average daily outdoor activity time fell below this recommendation among girls and among boys in Grades 1–3, suggesting that insufficient physical activity may emerge early rather than appearing abruptly at later developmental stages. Notably, sex differences became evident during elementary school, with girls in Grades 4–6 demonstrating significantly shorter outdoor time than boys.

Although boys in this age group met the recommended activity duration, girls did not, indicating a widening gender gap in physical activity during the school years. Sex differences became more evident during elementary school, with girls in Grades 4–6 demonstrating significantly shorter outdoor time than boys. These differences may be partially explained by variations in time use and social expectations. Previous national survey data in Japan [42] indicate that boys tend to spend more time in outdoor play, whereas girls are more likely to engage in indoor or home-based activities. Similar patterns have been reported internationally; for example, the Irish Neighbourhood Play Study found that boys were more likely to participate in outdoor play than girls [43]. Furthermore, the present findings are broadly consistent with previous studies conducted in urban settings, while also highlighting notable differences in activity patterns. Similar to findings from medium-sized cities in the Netherlands, sex differences became more pronounced after entry into primary school, with boys engaging in significantly more physical activity than girls [44]. These differences in time allocation and play preferences may limit opportunities for physical activity among girls. Furthermore, parental practices may differ by child sex, with parents of boys being more likely to allow independent outdoor play compared to parents of girls [45].

The present study, which focused on weekday behaviors, found substantially lower levels of physical activity. Specifically, average outdoor activity time was only 0.38 h among preschool children and 0.55 h among lower-grade elementary school children, both well below recommended levels. Compared with findings from urban populations in Spain [33], weekday activity levels in the present study were consistently lower across both preschool and early elementary school children. However, it should be noted that the present study did not assess weekend activity. As previous studies have shown that children’s physical activity levels often increase during weekends, the absence of weekend data limits direct comparability with studies that include both weekday and weekend measures. Nevertheless, the consistently low levels of weekday activity observed in this study indicate insufficient opportunities for daily physical activity in routine settings.

Importantly, reduced outdoor activity has been associated with a range of adverse health outcomes. Greater time spent outdoors has been shown to have a protective effect against myopia [46, 47], while insufficient physical activity is linked to poorer physical fitness and unfavorable weight status [48]. In parallel, the present findings revealed a clear increase in screen time with advancing school stage, particularly from Grade 4 onward. This pattern is consistent with previous international research showing that sedentary behavior increases from late childhood into adolescence. For instance, a large multinational study reported that higher screen time was associated with shorter sleep duration, later bedtimes, and lower levels of physical activity among children [32].Rather than reflecting individual motivation alone, these patterns may be shaped by developmental, social, and environmental factors that influence opportunities for outdoor play.

These findings may be interpreted in light of environmental and structural characteristics specific to rural settings. International evidence suggests that children in rural settings may exhibit less favorable activity patterns. For example, studies conducted in Taiwan and Iceland have reported that rural children tend to engage in more sedentary behavior and less physical activity during leisure time, with interactions observed between age and residential context in shaping activity patterns [49, 50].Within the Japanese context, several structural factors may contribute to these patterns. For instance, children in rural areas are more likely to commute to school by car compared with their urban counterparts [50]. Access to outdoor play spaces, such as parks and sports facilities, often depends on motorized transportation, and parental support plays a critical role in facilitating such activities [51]. From a public health standpoint, identifying such developmental periods of divergence is important, as they may represent critical windows for timely preventive intervention.

The present findings revealed a clear school-stage–related increase in screen time.

Notably, screen time began to increase significantly from Grade 4 in primary school and continued to rise throughout junior high school in both sexes, exhibiting an almost fourfold increase across developmental stages (from 1.46 to 5.70 h/day, p < 0.001). This pattern indicates a progressive consolidation of screen-related behaviors with age. The marked increase in screen time observed in this study is consistent with previous international findings. Evidence from previous studies have demonstrated that sedentary behavior and screen time increase from late childhood into early adolescence [52, 53]. In addition, the increasing availability and accessibility of digital devices may further contribute to this trend. As internet penetration continues to rise, children are being exposed to digital media at progressively younger ages. For example, a survey of primary school pupils reported that 40.1% had started using smartphones by 2018 [54], and national data indicate that internet usage among primary school pupils exceeded 81% in 2023 [55]. As a result, this developmental stage may represent a critical period during which screen time begins to increase more rapidly. This developmental trajectory warrants particular attention, as accumulating evidence suggests that prolonged screen exposure is associated with a range of interrelated lifestyle behaviors [56], including reduced physical activity [57, 58], shorter sleep duration and delayed sleep onset [56], and unhealthy dietary patterns [59].

Furthermore, when compared with previous findings from urban populations in Spain, the present results reveal both similarities and differences across age groups. Among preschool children (3–5 years), the average screen time observed in this study (1.74 h/day) was comparable to that reported in urban samples [33], where weekday sedentary time has been shown to exceed recommended limits (approximately1.58–1.78 h/day). This suggests that excessive screen exposure may already be prevalent at an early age, regardless of residential context. In contrast, more pronounced differences emerged among early elementary school children. Previous studies have reported that weekday screen time among children aged 6–7 years generally remains within recommended limits, with increases primarily observed during weekends. However, in the present study, average screen time among children in Grades 1–3 reached 2.89 h/day, exceeding recommended thresholds and approaching levels typically observed during weekends in urban populations.

These findings suggest that, in rural settings, elevated screen time may not be limited to leisure periods but may extend across the entire week. This pattern may reflect reduced availability of alternative recreational activities, as well as greater reliance on screen-based entertainment in daily routines.

The observed increase in screen time from Grade 4 onward may partially coincide with structural changes in the school curriculum, including a modest increase in instructional hours [60]. However, developmental transitions and increasing autonomy in media use are also likely contributing factors. Previous studies have reported that longer screen time is associated with increased nighttime snacking and evening-type tendencies [61]. Even moderate screen exposure has been linked to sleep onset difficulties [62, 63]. In this context, the relatively shorter screen time observed in preschool and early elementary school children may represent a protective window, during which healthy screen-use habits can be established before screen exposure markedly increases with age.

In rural regions such as Kochi Prefecture, additional structural constraints—including school consolidation [19, 40], limited transportation options, and reduced access to recreational facilities [51, 64]—may further restrict opportunities for outdoor and social activities. Within this demographic and educational context, children’s daily routines and opportunities for healthy behaviors may be increasingly shaped by structural and environmental constraints. Given this demographic and educational structure, coordinated efforts among the community, families, schools, and local government are essential to promote healthy child development throughout the prefecture.

More specifically, schools could incorporate structured opportunities for regular physical activity and provide education on healthy screen use and sleep habits. Parents or guardians play a central role in shaping children’s lifestyle behaviors. At the family level, promoting consistent daily routines—such as limiting screen exposure, encouraging regular physical activity, and maintaining stable sleep schedules—may support healthier behavior patterns. At the community level, improving the accessibility and safety of existing outdoor spaces may help facilitate increased physical activity among children. In rural settings, this may include addressing transportation barriers and enhancing the usability of local environments for active play. In addition, local governments could support these efforts through public health initiatives and community-based programs aimed at promoting balanced lifestyle behaviors, including appropriate screen use and healthy sleep practices.

Limitations

Several limitations of this study should be acknowledged. First, the cross-sectional design precludes causal inference regarding the relationships between age, lifestyle behaviors, and their developmental trajectories. Although school stage differences provide important insights into when unhealthy patterns may emerge, longitudinal studies are needed to confirm the persistence and causal pathways of these behaviors across childhood and adolescence. Second, lifestyle behaviors such as sleep duration, outdoor activity time, and screen time were assessed using parent- or self-reported measures, which may be subject to recall bias or social desirability bias. In particular, socially desirable behaviors such as outdoor activity time and sleep duration may be over-reported, whereas less desirable behaviors, such as screen time, may be under-reported. These reporting tendencies could lead to an underestimation of unhealthy behavior patterns. However, these measures are commonly used in large-scale epidemiological studies and remain practical tools for assessing children’s daily routines across a wide age range. Third, the study was conducted in a single rural prefecture in Japan, which may limit the generalizability of the findings to urban areas or other regions with different demographic and environmental characteristics. Nevertheless, focusing on a single community allowed for the examination of school stage patterns within a shared social and environmental context, which represents a key strength of the study. Finally, although outdoor activity time was used as a proxy for physical activity, it does not fully capture activity intensity or context; future studies incorporating objective measures of physical activity may provide a more comprehensive understanding of children’s movement behaviors. In addition, lifestyle behaviors were assessed using brief, single-item measures, which may not fully capture the complexity of children’s daily routines. The questionnaires used in this study were not formally validated, which may affect the reliability and comparability of the findings. Furthermore, data were collected only for typical weekdays, and behaviors on weekend days were not assessed, potentially limiting the representativeness of the reported patterns. Future studies employing comprehensive and validated instruments, as well as assessments across both weekdays and weekends, are warranted to confirm and extend these findings.

Conclusions

Taken together, these findings highlight that sleep, physical activity, and screen-related behaviors appear to develop sequentially across childhood within a shared rural environment. By examining school stage patterns across multiple developmental stages, the present study underscores the value of a life-course approach for identifying when unhealthy lifestyle behaviors first emerge and how they evolve over time. Such evidence may help inform the timing and focus of public health strategies aimed at promoting healthier daily routines among children living in rural regions.

Authors’ contributions

Conceptualization and supervision: H.S., N.H., A.M and J.L. Methodology, data collection, and analysis: H.S and A.H. Writing draft: H.S, N.H., A.M. Draft Revision: H.S., N.H., A.M., J.L. All authors have read and approved the manuscript.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

The datasets of the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study has been approved by the Ethics Committee of the Waseda University Institutional Review Board (Approval Number: 2021-H043). All participants or their guardians read a comprehensive explanation of the research process prior to participation and signed informed consent forms. The research process was conducted in accordance with the Declaration of Helsinki.

Consent for publication

Not applicable. This manuscript does not contain data from any individual person that would require consent for publication.

Competing interests

The authors declare no competing interests.