The goal of this clinical trial is to learn whether an online family health education program can help Vietnamese children aged 7-9 years with overweight or obesity develop healthier habits.

The main questions it aims to answer are:

1. Does the program improve parents' confidence, role modeling behaviors, family communication, and healthy family practices?
2. Does the program improve children's eating habits, physical activity, screen time, and body measurements related to overweight and obesity?

Researchers will compare the online family health education program with standard health education materials to see whether the program leads to greater improvements in children and their families.

Participants will:

1. Complete surveys about their family's health habits and daily routines.
2. Attend health checkups that include measurements of height, weight, and waist size.
3. Receive either the online family health education program or standard health education materials.
4. Complete follow-up assessments after the program and four months later.

The results of this study may help identify effective ways to support families in managing childhood overweight and obesity in Vietnam.

Childhood overweight and obesity have become increasingly prevalent in Vietnam and represent an important public health challenge. Children aged 7-9 years are at a developmental stage in which lifestyle habits, including dietary patterns, physical activity, and screen-related behaviors, are becoming established. At the same time, children remain strongly influenced by parental guidance and behavioral modeling. Parents therefore represent a key target for interventions designed to improve obesity-related behaviors and health outcomes among school-age children.

This study was conducted to develop and preliminarily evaluate a culturally adapted web-based parental role modeling program for parents of Vietnamese children aged 7-9 years with overweight or obesity. The intervention was designed to strengthen parental capacity to support healthy lifestyle behaviors within the family environment through education, behavioral practice, and ongoing digital support. The program was guided primarily by Social Cognitive Theory, which emphasizes observational learning, role modeling, reinforcement, and self-efficacy as mechanisms of behavior change. Bowen's concept of differentiation of self was incorporated into selected intervention activities to support parental emotional regulation, effective communication, consistent rule-setting, and maintenance of healthy family routines.

The study was conducted in two phases.

1. Phase 1: Development of the Web-Based Parental Role Modeling Program

   The intervention was developed using the ADDIE instructional design framework, consisting of Analysis, Design, and Development phases.

   During the analysis phase, a comprehensive literature review was conducted to identify evidence-based strategies related to childhood obesity management, parental role modeling, family-based behavioral interventions, and web-based health education. In addition, semi-structured interviews were conducted with 10 parents of children aged 7-9 years with overweight or obesity to explore educational needs, barriers to healthy lifestyle practices, family routines, caregiving challenges, and preferences for digital learning. Findings from the literature review and needs assessment were used to determine intervention priorities, learning objectives, educational content, and delivery strategies.

   During the design phase, a theory-based intervention framework was established. Program objectives, educational strategies, module sequencing, learning activities, and digital delivery methods were developed. The intervention consisted of six educational modules delivered over an 8-week period, followed by a 4-month maintenance and observation phase. Module content addressed childhood overweight and obesity, healthy nutrition, physical activity promotion, reduction of sedentary behaviors and recreational screen time, parental role modeling, family communication, family routines, and maintenance of long-term behavior change.

   During the development phase, educational materials and the Learning Management System (LMS) were created. Program materials included educational videos, presentations, quizzes, practical family activities, posters, visual reminders, and downloadable learning resources. Expert review was conducted to assess content validity, cultural appropriateness, practical applicability, and theoretical alignment. Prototype testing and usability testing were subsequently conducted with parents and experts, and revisions were made before implementation.

2. Phase 2: Feasibility and Preliminary Evaluation

   The evaluation phase employed an explanatory sequential mixed-methods design consisting of a quantitative quasi-experimental study followed by qualitative exit interviews.

   The quantitative component used a non-equivalent control group pretest-posttest design. Participants were recruited from five elementary schools in Hai Phong, Vietnam. Eligible participants were parents or primary caregivers of children aged 7-9 years with a BMI-for-age z-score ≥ +1 SD according to the World Health Organization growth reference. Parents were required to have access to the internet and digital devices and to be responsible for the child's daily routines related to eating, physical activity, and screen use.

   Children with chronic medical conditions, physical disabilities, developmental disorders affecting growth or lifestyle behaviors, families already participating in obesity-related programs, and parents unable to commit to the study schedule were excluded.

   Because randomization was not feasible, schools were allocated to either the intervention or control condition prior to participant recruitment to minimize contamination between groups. Parents recruited from intervention schools received the web-based parental role modeling program, whereas parents recruited from control schools received standard printed health education materials.

   A total of 60 parents were enrolled, with 30 allocated to the intervention group and 30 allocated to the control group. One participant withdrew from the intervention group during the study, resulting in a final sample of 59 participants.

   • Intervention Procedures

   Participants in the intervention group attended an online orientation session before beginning the program. During this session, parents received instructions on accessing the LMS, completing learning modules, participating in quizzes and activities, monitoring progress, and using the Zalo platform for communication and support.

   Parents then completed six web-based educational modules over an 8-week intervention period. Educational content was delivered through videos, presentations, quizzes, self-monitoring activities, and practical family-based exercises. Reminders and notifications were delivered through both the LMS and Zalo to encourage participation and adherence. Parents were also able to communicate with the research team through discussion forums and messaging functions.

   During the subsequent 4-month follow-up period, booster support activities were provided to reinforce learning and support maintenance of behavior change. These booster activities included online workshops, webinars, posters, infographics, and visual educational materials focusing on healthy nutrition, physical activity, family routines, and parental role modeling.

   Participants in the control group received printed educational materials related to healthy lifestyle practices but did not receive access to the LMS, online modules, or booster activities.

   Outcome Assessments:

   Data were collected at four time points:

   • Baseline before intervention (T0)

   • Immediately after completion of the 8-week intervention (T1)

   • One-month follow-up (T2)

   • Three-month follow-up (T3)

     * The primary focus of evaluation was feasibility.

   Primary feasibility outcomes included recruitment rate, retention rate, module completion rate, adherence to intervention activities, data completeness, usability, acceptability, participant satisfaction, perceived burden, and intervention-related adverse events. Predefined feasibility criteria were established before study implementation.

   * Secondary and exploratory outcomes included both parent-level and child-level outcomes.

   Parent-level outcomes included:

   - Parental self-efficacy

   - Parental role modeling of healthy eating

   - Parental role modeling of physical activity

   - Family communication patterns

   - Parental stress

   Child-level outcomes included:

   • Fruit and vegetable consumption
   • Physical activity behaviors
   • Recreational screen-time behaviors
   • BMI-for-age z-score
   • Waist circumference

   Anthropometric assessments were conducted by trained research personnel using standardized procedures. Height, weight, and waist circumference measurements were obtained at Hai Phong University of Medicine and Pharmacy Hospital. BMI-for-age z-scores were calculated using WHO growth references for children aged 5-19 years.

   * Qualitative Evaluation

   Following completion of the quantitative phase, purposive sampling was used to recruit intervention participants for individual semi-structured exit interviews. Interviews explored participant experiences with the LMS platform, perceived usefulness of program content, changes in parenting practices and family routines, barriers and facilitators to participation, satisfaction with the intervention, and recommendations for future improvement.

   Interviews were conducted face-to-face, audio-recorded with participant consent, and lasted approximately 30-45 minutes. Qualitative data were analyzed using thematic analysis. Findings from the qualitative phase were integrated with quantitative findings during interpretation to provide a more comprehensive understanding of intervention feasibility, acceptability, implementation processes, and potential mechanisms of behavior change.

   This study was designed to determine whether a culturally adapted web-based parental role modeling intervention is feasible, acceptable, and potentially effective for supporting healthy lifestyle behaviors and obesity management among Vietnamese primary-school children with overweight or obesity. Findings will inform the design of future large-scale randomized controlled trials and the development of scalable family-based childhood obesity interventions in Vietnam.

Inclusion Criteria:

• Parents of children aged 7-9 years with a BMI-for-age z-score ≥ +1 standard deviation (SD) according to the World Health Organization growth reference.
• Willingness to participate in a web-based program, including attending online workshops and completing behavioral tasks and assessment.
• Availability of the internet and digital devices necessary to engage in the web-based program.
• Parents who were responsible for the child's daily health-related routines, including meals, physical activity, and screen-time management.

Exclusion Criteria:

• Children with chronic medical conditions, physical disabilities, or developmental disorders that significantly affect dietary or physical activity behaviors or growth.
• Parents who are unable to commit to the study timeline or program schedule.
• Families already participating in another obesity-related program.

Beginning 6 months after publication of the primary study results and continuing for up to 5 years following publication.

De-identified individual participant data, study protocol, statistical analysis plan, informed consent form, and analytic code will be available to qualified researchers who submit a methodologically sound research proposal. Requests will be reviewed by the study investigators and approved if consistent with the study objectives, ethical requirements, and participant confidentiality protections. Approved researchers will receive access to the requested materials through secure electronic transfer.