The aim of the present study was to examine the effect of the ToyBox-intervention on Belgian four- to six-year-old preschoolers’ objective PA levels. Differences in PA outcomes were investigated from baseline to follow-up. Kindergarten-based and family-involved components were used in the intervention to achieve the goal of increasing preschoolers’ PA levels. At the kindergarten level, teachers had to implement the PA intervention component and received a manual in which environmental changes in the classroom, PA sessions, and classroom activities were described. To involve parents/caregivers at the home environment, educational materials (newsletters, tip-cards, poster) were provided to the parents/caregivers to introduce them with strategies and tips and tricks to increase their child’s PA levels. It was expected that the intervention would increase preschoolers’ PA of different intensities, whereas PA levels from preschoolers from the control group would stagnate.
In the total sample, intervention effects were found for VPA and MVPA during after school hours. There was a 0.3 and 0.4% increase in the intervention group for VPA and MVPA during after school hours compared to a stagnation in VPA and a 0.5% decrease in MVPA in the control group. Taking an accelerometer wearing time of four hours during after school hours into account, this 0.3% and 0.4% increase in VPA and MVPA corresponds to an additional 0.7 and 0.9 minutes of VPA and MVPA during after school hours. These small increases in VPA and MVPA during after school hours were also reflected in the small effect sizes. Additionally, borderline significant effects were found for VPA on a weekday and MVPA on an average day, with the intervention group having a 0.4% increase in VPA and a 1.2% increase in MVPA. Assuming an average accelerometer wearing time of ten hours per day, this 0.4% and 1.2% increase in VPA and MVPA respectively, corresponds to an additional 2.4 and 7.2 minutes of VPA and MVPA. Although these intervention effects for the higher intensities of PA were statistically significant in the total sample, the biological relevance should be interpreted with caution since it is unclear whether this small increase in VPA and MVPA will cause a health effect in preschool children.
Further, changes in PA between the intervention group and control group from baseline to follow-up were different for boys and girls. During after school hours, boys from the intervention group had a 1.0% increase in time spent in VPA and MVPA whereas time spent in VPA and MVPA in boys from the control group stagnated and declined, respectively. The increase in higher intensities of PA in preschool boys was very small and was again reflected in the small effect sizes. In preschool girls, only borderline significant effects were found for total PA and LPA during school hours, with girls from the intervention group having a smaller decrease in time spent in total PA and LPA during school hours. This means that stronger intervention effects were found in boys compared to girls, which might indicate that more effort should be taken to involve preschool girls in PA interventions. A possible strategy might be to make changes in the current ToyBox-material to make it more attractive to preschool girls. At the moment, the classroom activity guide for PA consisted for a significant part of structured PA sessions which mostly consisted of higher intensity activities. Since preschool boys engage in activities with higher intensities compared to preschool girls [7, 11] and preschool boys are found to be more physically active in general , the ToyBox-material might have addressed preschool boys more compared to preschool girls.
Different effects were found for preschoolers from high versus low SES kindergartens, which means kindergartens located in high versus low SES neighbourhoods. In preschoolers from low SES kindergartens, negative intervention effects were found for time spent in total PA and LPA during school hours, with preschoolers from the intervention group having a steeper decrease from baseline to follow-up compared to the control group who had a smaller decrease in total PA and LPA. In contrast with the negative intervention effects in low SES kindergartens, we did find positive intervention effects for all PA outcomes in high SES kindergartens. Since kindergarten SES was based on SES of the municipality, it might be plausible to say that low or high SES kindergartens were located in low or high SES neighbourhoods. In high SES neighbourhoods, children have more opportunities to be physically active because of a higher access to a private garden at home and the availability of safe playgrounds in the neighbourhood . Children from low SES neighbourhoods have less access to a private garden at home, a park or suitable nearby nature . Furthermore, playgrounds in low SES neighbourhoods are more hazardous compared to playgrounds from high SES neighbourhoods . Therefore, it might have been easier for preschoolers’ parents/caregivers from high SES neighbourhoods to put the information from the newsletters and the tips and strategies from the tip-cards into practice. Furthermore, parents/caregivers from high SES neighbourhoods might perceive the traffic as safer , and together with the information from the newsletters and tip-cards this might have increased preschoolers’ active transportation to high SES kindergartens. Although the effects of low and high SES neighbourhoods on PA are understudied in this age group, this might be a possible explanation for the positive intervention effects on preschoolers’ PA from high SES kindergartens only.
In preschool girls and high SES kindergartens, most intervention effects were found for PA outcomes during school and after school hours. In girls and in high SES kindergartens, preschoolers from the intervention group had a smaller decrease in total PA and LPA during school hours compared to the control group. This decrease in total PA and LPA might be explained by the fact that preschool children have to learn to sit still in preparation of primary school , which might have caused a shift from total PA and LPA to sedentary time. However, this decrease was smaller in the intervention group in girls and children from high SES kindergartens, which means that the intervention had a positive effect on the decrease in total PA and LPA in girls and preschoolers from high SES kindergartens, and the implementation of the intervention might have counteracted the steep decrease of time spent in total PA and LPA during school hours. Furthermore, half of the preschool children at follow-up were going to the third kindergarten class (birth year 2007), which means that – in Belgium – they get the opportunity to participate in after school activities (i.e., structured activities out of school like preschool gymnastics, swimming classes, football). Since one study found a decline in physical activity when preschool children get older  and PA rapidly declines during childhood and adolescence , the participation in after school activities in older preschool children might have slowed down the decrease in LPA and total PA during after school hours in the intervention group.
Although Belgian preschoolers’ physical activity levels were measured during the same period (March-June 2012) at baseline and at follow-up (one year later; March-June 2013), the weather might partly explain the decrease in physical activity levels of preschoolers from the control group. During Spring 2012, the mean outside temperature was 10.5°C, whereas this was only 7.7°C during Spring 2013. In addition, there were more hours of sunshine during Spring 2012 compared to Spring 2013 (469 hours vs. 386 hours), and less rainy days (43 days vs. 47 days) with less rain in total (200.4 mm vs. 222.5 mm) (http://www.meteo.be). Other studies have also reported higher physical activity levels in preschool children when the weather is warmer or drier compared to colder and wetter weather conditions [44, 45].
A possible explanation for the fact that only small effects were found for the total sample of preschoolers after receiving the ToyBox-intervention might be that Belgian (Flemish) kindergartens already implement PA components into the curriculum. For example, preschoolers already receive structured PA sessions during the time they spend at kindergarten . In Flemish kindergartens, these sessions are scheduled in the curriculum for two hours per week to realize one of the developmental goals of the kindergarten curriculum prescribed by the Flemish government, namely physical education of the preschool child [13, 47]. In the ToyBox-intervention, preschool teachers had to implement the PA-module for at least one hour per week, which is shorter compared to the physical education sessions preschoolers already receive. This might mean that the intervention dose might have been too low to cause more effect in the total sample, as both intervention and control groups already received the two hours of physical education in the curriculum.
A detailed process-evaluation on the implementation of the PA-component of the ToyBox-intervention by both the teachers and the parents/caregivers might be needed to provide insights in and to draw meaningful conclusions on the outcome results. For example, an explanation for the limited intervention effects in the total sample could be the lack of kindergarten teachers’ motivation to spend time on increasing preschoolers’ PA levels due to time constraints and the full curriculum. Another explanation might be related to the implementation of the parental-involved component of the ToyBox-intervention. Preschoolers’ parents/caregivers received two newsletters, two tip-cards and a poster with tips and tricks to increase their child’s PA levels. Nevertheless, it might be possible that part of the preschoolers’ parents/caregivers did not read the newsletters and tip-cards, or that they did not carry out the tips and tricks at home. Since only materials were handed out to the parents/caregivers, there was only a passive parental-involved component in the ToyBox-intervention. In addition, actively involving parents/caregivers as intervention targets might be a promising factor in an intervention [18, 19, 22, 23]. Thus, intensifying the parental-involved component of the ToyBox-intervention possibly might lead to better effects. Finally, the time spent on PA during the ToyBox-intervention might have been too short (six weeks in total, but with the environmental changes implemented throughout the whole school year and the structured PA sessions implemented for 20 weeks) and/or the intensity might have been too low (a minimum of one hour per week) to expect changes in preschoolers’ PA levels. The short time and the low intensity spent on PA had two reasons. First of all, the ToyBox-intervention targeted four different behaviours, of which PA was only one. Therefore, only a limited amount of time (six weeks for each behaviour) was available to focus on preschoolers’ PA. Secondly, to enhance future implementation of the ToyBox-intervention, teachers had to implement the intervention instead of researchers. Consequently, the time asked to allocate to each of the intervention components was kept to a minimum, so that the implementation was more attainable for the teachers.
Study limitations include the use of different accelerometer models, and the relatively large drop-out of children due to the lack of valid accelerometer data. Strengths of the present study include the objective assessment of PA in a large sample of four- to six-year-old Belgian preschoolers, with the disposal of different PA intensities, and the randomized controlled trial with the pre-test post-test design including an intervention and control group.