This study protocol aims to analyze and compare the effects of combined movement and storytelling intervention (CMSI) on fundamental motor skills (locomotor skills and object control), language development (language comprehension, language expression, vocabulary and language description), and physical activity levels (light, moderate to vigorous intensity, and sedentary time) in children aged 3 to 6 years. The sample will consist of 144 children of 12 classes group, randomly assigned to 3 experimental groups (n= 72 children) and 3 control groups (n= 72 children), belonging to 4 classes group of upper middle level classes (2 experimental and 2 control), 4 transition level 1 classes (2 experimental and 2 control) and 4 transition level 2 classes (2 experimental and 2 control). The experimental groups will perform the CMSI for 3 sessions (40-minute per session) per week over 12-weeks (using one motor story per week), while the control groups will not receive any treatment. The main outcome will provide information about fundamental motor skills, language development, and physical activity levels. It is hypothesized that the CMSI has the potential to generate significant increases in selected assessments. If this intervention proves to be beneficial, if could contribute to preschoolers children curricula.

The study includes an experimental design (randomized controlled trial), double-blind, repeated measures and parallel groups (6 interventions and 6 controls) considering previous studies and a quantitative approach. The methodology followed will be the Consolidated Standards of Reporting Trials Statement (CONSORT) methodology.

It is expected to recruit 12 children from each classes group (without distinction of sex). The distribution of the classes groups (12 classes group) will be in 3 experimental groups (6 classes group, n ± 72 children) and 3 control groups (6 classes group, n ± 72 children). The distribution by clusters or strata is justified by the fact that the use of individual randomization would imply a high probability of contaminating the control groups, since it is unfeasible to prohibit children interaction in classrooms or school recreational spaces (i.e., playgrounds, hallways, laboratories), which is where the study intervention will be carried out. The sample size calculation indicates that the ideal number of participants per group is 10. As agreed in a previous study, a mean difference of 3.22 total score of locomotor skills domains was used for this calculation as the minimum difference necessary for substantial clinical relevance, with a standard deviation of 0.70 points, considering an alpha level of 0.05 with a power of 80% and an expected loss of 15%. The GPower program (version 3.1.9.6, Franz Faul, Universiät Kiel, Kiel, Germany) will be used to calculate the statistical power.

The 12 classes group will be selected in 4 upper middle level classes (2 experimental and 2 control; age range between 3 to 4 years), 4 transition level 1 classes (2 experimental and 2 control; age range between 4 to 5 years) and 4 transition level 2 classes (2 experimental and 2 control; age range between 5 to 6 years), which will be randomized by stratified sampling, which consists of segmenting the classes that agreed to participate in the study according to educational levels (strata) and then performing a random sampling on each one of them, using R statistical software, version 4.1.2. This study is considered double-blind because the measurements will be performed by professionals external to the research.

The investigators estimate the participation of 144 children residing in the Maule region, Chile who meet the following inclusion criteria: (i) be enrolled in the educational center (school, college or kindergarten) that commits to participate in the intervention; (ii) age range between 3 to 6 years old; (iii) attend ≥ 85% of the sessions scheduled for the combined movement and storytelling intervention (CMSI). As for the exclusion criteria, will be the following: (i) children with musculoskeletal injuries or medical contraindications (i.e., congenital heart disease, fever, diarrhea or general malaise) that would prevent their normal performance in the assessments and intervention and; (ii) children with permanent educational needs mentioned in Decree Nº83 of the Chilean Ministry of Education, such as, visual, hearing, intellectual or multiple disabilities, dysphasia or autistic disorder.

The current protocol has been reviewed and approved by the Scientific Ethics Committee of the Universidad Católica del Maule, Chile (approval number: N°105/2021, 04 August 2021) and developed following the Declaration of Helsinki for work with human beings.

Before starting the intervention, during the last week of March 2024 (for two weeks), children will be evaluated in the variables considered for the research, later, from the third week of March to the first week of June 2024 (12 weeks) will participate in CMSI. After the intervention (second week of June 2024), for two weeks, the children will undergo the same initial assessments.

Inclusion Criteria:

• Be enrolled in the educational center (school, college or kindergarten) that commits to participate in the intervention.
• Age range between 3 to 6 years old.
• Attend ≥ 85% of the sessions scheduled for the CMSI.

Exclusion Criteria:

• Children with musculoskeletal injuries or medical contraindications (i.e., congenital heart disease, fever, diarrhea or general malaise) that would prevent their normal performance in the assessments and intervention.
• Children with permanent educational needs mentioned in Decree Nº83 of the Chilean Ministry of Education, such as, visual, hearing, intellectual or multiple disabilities, dysphasia or autistic disorder.

Participant data will not be shared. The investigators will only disseminate the results of the study through scientific papers and presentations at scientific congresses.

The assessments will be scheduled two weeks before and after the intervention with a team of evaluators who will not have information about the training groups, nor will the participants know their identities. That is, a double-blind shield