This study recruited 366 physically and mentally healthy children from three kindergartens in Beijing and obtained informed consent from their parents/guardians before the study began. After excluding missing and invalid data, 358 children entered the follow-up analysis (194 boys and 164 girls). All children underwent anthropometry measurement, FMS, and PA tests. Ethical approval was obtained from the ethics committee of the School of Sport Sciences, Beijing Sport University.

Standing height was measured with a stadiometer (TZG, Shanghai). The stadiometer was calibrated before the test began. Have the child stand erect on the floorboard of the stadiometer with his or her back to the vertical backboard. The child’s buttocks, scapulae, and head are in contact with the vertical backboard. The child’s head is maintained in the Frankfort Horizontal Plane position. After the measurement is read, it should be recorded to the nearest 0.1 cm. Weight was measured with an electronic digital scale (HBF-255 T-W). Have the child stand on the center of the weight scale platform. Record the weight to the nearest 0.1 kg. Body Mass Index was calculated by formulation BMI=Weight/Height² (kg/m²). The child’s weight status was classified as normal, overweight, and obese by BMI (22).

Children’s FMS were evaluated using the Test of Gross Motor Development-2 (TGMD-2). The TGMD-2 evaluates children’s 6 locomotor skills and 6 object control skills. Locomotor skills include run, hop, gallop, leap, horizontal jump, and slide. Object control skills include striking a stationary ball (from a tee), stationary dribble, catch, kick, overhand throw, and underhand roll. Each skill was broken down into 3–5 components, and each component was scored as either a 1 or a 0. Examiners verbally guided and demonstrated each skill; then the child performed that skill twice. Examiners recorded and rated children’s performance, and sum raw scores for six locomotor skills (0–48) and sum raw scores for six object control skills (0–48) were calculated. Each examiner was trained and supervised by an experienced instructor. The intraclass correlation coefficient (ICC) was 0.94–0.98 on locomotor skills and 0.91–0.95 on object control skills.

Children’s PA levels were assessed using triaxial accelerometers (ActiGraph GT3X+) for 7 consecutive days. Parents and teachers were given verbal and written instructions on the proper use of the accelerometer and were asked to record children’s activities. The accelerometer was worn on the child’s right hip at the anterior superior iliac spine (ASIS), and the child was only allowed to remove it when showering or sleeping. The sampling frequency was 100 Hz, and activity counts were analyzed with 15 s/epoch (23). Only days worn time more than 600 min were considered valid, and children wore them for a mean of 10.7 ± 1.5 h. Zero activity periods of 20 min were interpreted as non-wear time, and counts <0/min or ≥ 15,000/min were excluded because these values are not considered biologically plausible (24). The valid days included in the analysis were 2 weekdays and 1 weekend. The cut-off point for vector magnitude proposed by Butte et al. was used to calculate the duration of low (820 < counts/15 s ≤ 3,907), moderate (3,907 < counts/15 s ≤ 6,111), and vigorous (counts/15 s > 6,111) intensity physical activity (25). Equipment initialization and data analysis were conducted by ActiLife software (version 6.13.3).

The data were analyzed in SPSS25.0 software. Descriptive statistics and frequency calculations were performed for demographic, anthropometry, PA, and FMS variables. A Chi-square test was used for comparative analysis of overweight/obesity rates between genders; an Independent Samples T-test was used for comparative analysis of PA levels and FMS levels between male and female preschoolers of the same age group; ANOVA and post hoc analysis were used to examine the differences in PA and FMS levels among ages in both genders; and a partial correlation analysis was used to investigate the correlation between BMI, PA, and FMS levels. Analysis of covariance (ANCOVA) was used to compare the BMI, PA, and FMS levels between normal and overweight/obese subjects, with a significance level of p < 0.05.

The overall trend of increasing duration of moderate-to-vigorous physical activity with age in this study may be because older children usually have higher cognitive levels and more mature physical development. Therefore, age is an important factor in young children’s participation in moderate-to-vigorous physical activity. Pate et al. found that boys participated in PA longer in total and moderate-to-vigorous intensity times than girls (27). The findings of other studies also support that boys are more active and involved in more moderate-to-vigorous physical activity than girls during early childhood (28, 29), similar to the present study results. This may be because boys are usually more active and better at all sports, giving them more opportunities to participate in sports longer. While girls are more involved in creative play and activities, such as drawing and painting, crafts, etc., thus increasing their LPA and sedentary time.

In terms of motor development levels, there were significant differences in motor development between all age groups and an overall linear trend of increase. Figure 1 shows that boys generally had better object control skills than girls, which is consistent with most studies (8, 30). This is because boys are more likely to engage in ball sports, which increases their mastery of object control skills. Bandeira reported that boys performed better in throwing and hitting skills (31), while Pablo’s results concluded that boys had a greater mastery of hitting and dribbling skills (32). Locomotor skills did not show regular gender differences, with girls outperforming only boys in the 5-year-old group. However, most studies in recent years have reported no significant differences in displacement skills between boys and girls (33–35), and some studies have reported that boys scored higher than girls in both locomotor and object control skills (36, 37). Support for the idea that girls’ locomotor skills are superior to boys’ may be due to the fact that girls develop earlier than boys, resulting in differences in physical capacity. As for the possibility of no gender differences in this study, it may be because in the preschool stage, children have similar physical development without gender advantages.

In addition, Figure 1 shows that the development of locomotor skills is faster than that of object control skills, which is mainly due to the fact that 3–6 years old is a crucial period for the development of large muscle motor skills, and compared to displacement skills, object control skills require more hand-eye coordination and control while examining the power of large muscles, which requires more attention, analysis, and use of external information (38). In addition, the test instrument selection is also crucial, as the TGMD-2 emphasizes the degree of movement completion, and each indicator corresponds precisely to each part of the limbs and trunk. However, due to cultural differences, Chinese children are less exposed to baseball-like movements, such as hitting a stationary ball with both hands and throwing a ball overhand in the object control skills category, which makes it more difficult to develop a mature movement pattern.

The results of this study showed that PA was significantly and positively correlated with both locomotor skills and object control skills. Studies have shown that FMS are closely related to PA, and FMS are a necessary foundation for physical activity. The development of physical activity can promote the improvement of fundamental movement skill ability (39, 40). Since this study was cross-sectional, it is difficult to determine whether higher levels of PA contributed to higher levels of FMS or higher levels of FMS contributed to higher levels of PA. However, in a longitudinal study of school-age children, Elizabeth et al., concluded that to increase PA engagement levels, FMS mastery is needed, rather than increasing the time spent on PA to increase FMS mastery (41). Similarly, Crane and his colleagues have identified the development of FMS in early childhood as a key behavioral determinant of PA habits and noted that developing FMS early in life provides a stimulus for developing lifelong PA (42). Thus, understanding the relationship between FMS and PA in early childhood can help us further research to improve lifelong PA. In addition, most studies similarly consider proficiency in FMS as a prerequisite for improving PA, as learning locomotor skills is necessary for participation in PA (43).

Regular physical activity (activity that consumes energy through skeletal muscle contraction) is an effective means of promoting children’s physical and mental health development, and can effectively reduce the incidence of obesity and a series of diseases caused by obesity (44). Studies have concluded that overweight/obese children have lower levels of PA and longer sedentary time compared to their normal-weight peers (45, 46). Still, no significant relationship between BMI and PA was found in this study (as shown in Table 3). In further gender comparison of normal and overweight obese children, no significant difference in PA levels was found between normal-weight and overweight/obese boys. Still, normal-weight girls spent significantly more time on vigorous physical activity and less time on sedentary time. The gender differences may be due to the influence of socialization factors, where children participate in specific types of activities by gender, including free play and structured activities (47–49). In addition, studies have confirmed that girls have higher self-esteem in early childhood than boys (45–50). For overweight and obese girls, although motor development does not differ significantly from that of girls of the same age, demonstrated ineptitude or “clumsiness” in movement tends to affect their self-esteem. It leads them to stop or abandon PA, thus choosing activities with lower levels of PA or longer sedentary time. Therefore, it was found that preschool girls’ PA levels were more likely to be influenced by their weight status.

This study found no statistically significant association between the level of FMS development and BMI in young children. Previous studies have had inconsistent findings regarding the relationship between preschoolers’ weight status and their FMS development level. It is generally assumed that children with a high BMI have lower levels of FMS because being overweight typically has a more significant influence on running, jumping, and items that require dynamic body coordination (51–53). In addition, a higher level of FMS in children can improve their ability to participate in other PA, and the improvement of PA ability can help maintain a healthy weight. However, in a study of young Chinese children using the TGMD-2 test, FMS were not correlated with BMI (54), and other studies have supported the idea that the two are unrelated (21, 55). It may be that preschool children have not fully learned and mastered these fundamental movement skills (56), thus not effectively improving their PA level, which results in no significant relationship with BMI.

Stodden et al. proposed a theoretical model of the relationship between PA, FMS, perceptual-motor skills, health-related physical fitness, and obesity in children (13). It is emphasized that PA is an important moderator of FMS and obesity, but the effects of other moderating variables are equally important. This study did not find a relationship between FMS and BMI, this may be because the influence between these factors is a dynamic interaction process over a long period. The young age of preschool children, who were the subject of this study, maybe the reason for the absence of a significant relationship. The development of FMS is sustainable (57), and there is growing evidence of a moderate-to-strong positive correlation between enhanced levels of FMS with age and physical fitness, particularly in adolescence (58, 59).

Although this study explored the relationship between BMI, FMS, and PA in preschool children, there are several limitations that need to be addressed. Firstly, due to the cross-sectional design of this study, it was not possible to examine the reciprocal effects among the three factors. Future longitudinal studies are needed to gain a better understanding of the interplay among these factors. Additionally, the use of BMI to classify weight status has limitations as it cannot distinguish between body fat and lean body mass (60). Therefore, for further research on children, body fat measurement (such as using a skinfold caliper) should be used instead of BMI to measure weight status.