ENTREN-F Programme describes a novel structured psychosocial family-based intervention from Primary Care using a train trip metaphor aimed at improving healthy lifestyles for the whole family. It is oriented to children aged 8-12 years old who have overweight or obesity. The ENTREN-F intervention lasts 6 months and consists in 12 biweekly 2-h2 sessions in group, following a multidisciplinary perspective.

The main aim is to examine the efficacy of the intervention program 'ENTREN-F' (intervention for children plus family intervention) on anthropometrics, behaviour, psychological and family factors, from a multidisciplinary perspective, compared with another group participating in the same program 'ENTREN' (intervention for children without family intervention) and with a control group (usual treatment) among Spanish children with overweight and obesity. Finally, (2) the second aim was to evaluate whether the changes were maintained 6, 12 and 18 months after the end of the intervention.

Hypothesis The specific hypotheses of the present study were as follows: (a) There will be significant differences in the adherence to treatment, being higher in the ENTREN-F group (b) There will be improvements in clinical outcomes regarding the anthropometric variables of the child, the level of physical activity, psychological distress, and eating disorder of the child, after both interventions (ENTREN and ENTREN-F programme), in comparison to control group (d) There will be only improvements in clinical outcomes regarding in the family's healthy life-style, psychological distress of the parents, and the family environment, after the intervention of the ENTREN-F programme. (e) The significant changes produced will remain stable at the 6,12 and 18-month follow-up in the ENTREN-F group.

Sample: The sample will be made up of 240 children of 8-12 years old (IMC>P90). The dropout rate is expected to be 20%. The majority of the participants will be recruited through Primary Health Care Services, in collaboration with Paediatrics Area. A small percentage of the sample contacted the program after receiving information from their school or advertising posters. After assessment, they are assigned randomly to one of the three conditions.

For Patient Registries:

• Spanish Ministry of Economy, Industry and Competitiveness provides an annual quality assurance for monitoring and auditing all financial projects (4-yr). This plan addresses data validation and registry procedures.
• A review of databases is regularly scheduled.
• Sample size assessment has been verified, specifying the number of participants necessary to demonstrate an effect (size effect; N=240). Regarding the sample size, assuming a two-tailed test α = .05 and a power (1 - β) of .80, estimating a 23% difference in the prevalence rates of childhood obesity, and applying a correction of according to the guidelines of Browner, Newman, Cummings and Hulley (2007) to anticipate a possible sample loss of approximately 20%, based on the study by Robertson (2008), a sample size of 80 children per group has been estimated (n = 240). Therefore, it is expected to collect substantial changes with an N = 60 in each of the groups at the end of the 12-month follow-up.
• A preliminary statistical analysis plan has been described with the analytical principles and statistical techniques to be employed in order to address the primary and secondary objectives, as specified in the study protocol or plan. A preliminary plan for missing data has also taken into account and missing values will be taken into account in analyses. An expert methodologist collaborates in the Project and advises us in this field of work.
• Standard operating procedures to address registration operations and analysis activities, such as patient recruitment, data collection, data management, data analysis, adverse event reporting, and change management. All members of the Project has received a specific training by A.R.S.
• A data dictionary that contains detailed descriptions of each variable used by the registry, including the source of the variable, coding information if used and normal ranges if relevant. This document is provided to the principal members of the team.

Assessment: The clinical evaluation consists in an interview where socio-demographic and family clinical variables are evaluated, the semi-structured child diagnostic interview is carried out (K-SADS-PL) based on Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria and a battery of questionnaires are administered to the child and both parents. Assessment are carried out over time (T0 baseline vs. T1 post/6-month vs.T2, T3 and T4, 6, 12 and 18-month follow-up, respectively).

Multidisciplinary team: Most of the sessions of the psycho-family sessions workshop group and the psychological workshop group with children are conducted by psychologists, with at least Clinical Psych MSc, some of them also doing Clinical Psych PhD. All therapists have received specific training prior to the protocol and work from Motivational Interview perspective. The team also has a nutritionist, psychiatrist and an expert in physical activity, training in Motivational Interview. Finally, paediatricians and nurses from the health centres in the area collaborate actively in the Project. Meetings for feedback about the progress of the project and annual specialist seminars are organized. The results and progress are also shared in Paediatrics and Psychology conferences. A multidisciplinary project from Primary Care, combining the joint effort of different professionals that allows a rapid and effective overweight patient care protocol to be developed. Interest has grown in the Project by international PhD students and Postgraduate students as evidenced in their project collaboration and consequent training.

Relevance of the study: Overall, this project will represent a significant contribution to the scientific understanding of this field as well as a significant savings in economic costs derived from this illness. It is expected to have an important clinical impact in the Madrid region, providing assistance to 240 families in the hospital. This is a pioneer research project that examines the efficacy of the new program of psychosocial family-based intervention for childhood overweight and obesity within Primary Care. The innovation and creativity of the ENTREN program for children highlights the broad content in emotional self-regulation, which has two aims: it helps to overcome the emotional difficulties (frustration, anxiety, impatience) and modify their eating habits, in turn, it could help to reduce the onset of unhealthy eating patterns or their prevalence (binge eating, emotional eating, picking). In addition, it highlights the inclusion of the family as a key factor in the change and implement of healthy lifestyles in children with overweight/obesity. The programme ENTREN-F (pilot study results) has been awarded by the Ministry of Health and Consumer Affairs, Strategy for Nutrition, Physical Activity and Prevention of Obesity (NAOS annual Award) in December 2017.

Ethical approval: The study received ethical approval by the Child and Adolescent Hospital Niño Jesús (Ref. R-0058/16), Central Committee of Research, Primary Care Commission (Ref. 32/17; 13.12.17) and Autonomous University Ethics approval (CEI-76-1394).

Inclusion Criteria:

1. Age between 8-12 years
2. BMI > Percentile 90
3. Presenter of physical and cognitive development according to sex and age
4. Good understanding of Spanish orally and in writing.
5. Do not present any difficulty that prevents the performance of autonomous physical activities

Exclusion Criteria:

1. standing obesity caused by a genetic syndrome
2. the child or none of their primary caregivers do not have adequate command of oral or written Spanish

a) Intellectual disability b) dieting supervised by an endocrine specialist at the time of the evaluation c) To suffer a serious psychological or medical disorder that requires immediate intervention d) Do not present excess weight as a side effect of a pharmacological treatment that could act as a confounding variable.

The study protocol is available. The structure of the program and the specific content of the sessions will be available in a published guidebook. Upon prior request, a document with the interpretation of the items in Statistical Package for the Social Sciences (SPSS) databases, a description of the instruments and outcomes variables included in this study, may also be provided. PhD. Ana Rosa Sepúlveda will be the responsible of reviewing all request, and taking a final decision. Criteria for reviewing requests: National and international Research Groups related to childhood obesity or eating disorders. Types of analyses: replica of ENTREN's Randomised controlled trials (RCT) in other countries or meta-analyses studies.

IPD will become available from December of 2021. Period of availability: unlimited after publication. Request and a revision of the request are both necessary conditions.

The study protocol will also be available. The structure of the program and the specific content of the sessions will be available in a published guidebook. Upon prior request, a document with the interpretation of the items in SPSS databases, a description of the instruments and outcomes variables included in this study, may also be provided. PhD. Ana Rosa Sepúlveda will be the responsible of reviewing all request, and taking a final decision. Criteria for reviewing requests: National and international Research Groups related to childhood obesity or eating disorders. Types of analyses: replica of ENTREN's RCT in other countries or meta-analyses studies.