Here is the design of a clinical trial:

Official Title: Parents and Children Active Together: Examining Motivational, Regulatory, and Habitual Intervention Approaches

Included conditions:
- Physical Activity

Study Armgroups:
- {'label': 'Standard education control group', 'type': 'NO_INTERVENTION', 'description': "The control group package will consist of Canada's PA guidelines recommending 180 min per week for young children, transitioning to 60 minutes of activity a day for children at five and a breakdown of ways for the parent to help their child achieve this PA (unstructured, endurance, strength, activities) commensurate with this guide. The guide also contains arguments and information about the benefits of PA."}
- {'label': 'Physical activity planning intervention', 'type': 'OTHER', 'description': 'The physical activity planning intervention condition will receive the same guidelines as the standard education control group but will also be provided with family physical activity planning material. This material will include workbook on how to plan for family physical activity; brainstorming exercise for children where they list physical activities that they have found fun in the past, as well as activities that they would find enjoyable to do as a family.', 'interventionNames': ['Behavioral: Physical activity planning intervention']}
- {'label': 'Habit formation intervention', 'type': 'OTHER', 'description': 'The habit formation intervention condition will receive the same content as the education control condition and the physical activity planning condition but with additional material on creating physical activity support habits. The material includes a brief discussion of what habits are with some very straightforward examples such as preparing for sleep routines, or initiating to drive a car to work. A key component of the habit section will be based on planning for context-dependent repetition, with pointers on how to maintain repetition as habit forms.', 'interventionNames': ['Behavioral: Habit formation intervention']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Habit formation intervention', 'description': 'In addition to the control content and the planning content, this intervention will include material provided to the family that assists with creating physical activity support habits. The material contains a discussion of what habits are, straightforward examples, planning and pointers for forming habits. A key component of the habit intervention will be planning for context-dependent repetition.', 'armGroupLabels': ['Habit formation intervention']}
- {'type': 'BEHAVIORAL', 'name': 'Physical activity planning intervention', 'description': 'This arm will receive the control education content, but will also be provided with family PA planning material. This material will include skill training content (workbook on how to plan for family PA). The material includes a brainstorming exercise for parents where they list physical activities they think their children have found fun in the past, as well as activities that they would find enjoyable to do as a family. We also have Canadian parental survey data on the most preferred co-physical activities for children 3-6. We will provide this material as prompts/suggestions. This list helps create the template for PA planning by contextualizing what the parents would like to do with their kids.', 'armGroupLabels': ['Physical activity planning intervention']}

Primary Outcomes:
- {'measure': "Change from baseline in children's physical activity to 6 months", 'description': "Children's physical activity will be quantified by accelerometry. Children will wear an accelerometer for a minimum of 6 hours per day for 7 days at baseline and 6 months. Additionally this measure will assess intermediate outcomes at 6 weeks and 3 months.", 'timeFrame': 'Baseline and 6 months'}

Please estimate the sample size based on the assumption: 
4 repeated assessments, 3 groups, a power of .90, an alpha of .05, and an anticipated attrition rate of 15%.
Justification of sample size
        G-Power (Version 3.1.9.2) was used to calculate sample size. With 4 repeated assessments, 3 groups, a power of .90, an alpha of .05, effect sizes ranging from .25 to .30, and an anticipated attrition rate of 15% [34], a minimum of 165 families with a goal of 240 families (i.e., 55â80 families per condition) are needed to show a significant difference in physical activity accelerometry (minutes of MVPA primary outcome) by condition over time. The effect sizes represent the findings from our prior intervention research comparing planning to education with this demographic [34] and considering our pilot study on habit formation [42], yet it is clearly in the clinically meaningful range for the detection of differences between the planning and habit formation conditions [107, 108]. However, detection is dependent on the performance of the habit versus planning conditions which is largely unknown.