Here is the design of a clinical trial:

Official Title: The SmartFeeding4Kids, a Web-based Food Parenting Intervention to Promote Positive Feeding Practices and Healthy Diet in Preschool Children, Through Self-regulation and Behavior Change Techniques: a Randomized Control Trial

Included conditions:
- Parental Feeding Practices and Children's Healthy Diet

Study Armgroups:
- {'label': 'SmartFeeding4Kids', 'type': 'EXPERIMENTAL', 'description': "SmartFeeding4Kids: information about children's healthy diet and effective parental feeding practices, with a behavioral intervention (5 sessions plus 2 brief booster sessions online intervention)", 'interventionNames': ['Behavioral: Behavioral change intervention;', 'Behavioral: Health Education']}
- {'label': 'SmartFeeding4Kids Health', 'type': 'ACTIVE_COMPARATOR', 'description': "Psychoeducational condition: information about children's healthy diet and effective parental feeding practices (5 sessions plus 2 brief booster sessions online intervention)", 'interventionNames': ['Behavioral: Health Education']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Behavioral change intervention;', 'description': "Behavioral change intervention: goal setting, regarding child's diet and parental feeding practices; self-monitoring, with observation and recording of the child's food intake and parental feeding practices; individualized feedback, based on preceding week monitoring and according to the defined objectives, regarding child's and parent's behaviors; modeling and direct suggestions by tailored parent figures; positive reinforcement associated to parents' accomplishment of the objectives; prompts, to remember the defined objectives and the main messages of the intervention.", 'armGroupLabels': ['SmartFeeding4Kids']}
- {'type': 'BEHAVIORAL', 'name': 'Health Education', 'description': "Health education: provision of information about preschool children's nutrition guidelines, effective parental feeding practices, strategies to overcome food and feeding-related barriers, and steps to form healthy habits.", 'armGroupLabels': ['SmartFeeding4Kids', 'SmartFeeding4Kids Health']}

Primary Outcomes:
- {'measure': "Changes from baseline in the child's dietary intake reported by parents", 'description': "Child's dietary intake reported by parents: Child's dietary intake is evaluated through a 24h food recall, completed during 3 days (two weekdays and one weekend day). Data regarding the mean number of portions of vegetables, fruit, and sugar-sweetened foods and beverages registered on three days will be extracted from the database and analyzed separately as primary outcomes.", 'timeFrame': 'Baseline, immediately after the intervention, 3 months after the intervention, 6 months after the intervention'}
- {'measure': 'Changes from baseline in parental feeding practices', 'description': "Parental feeding practices: Parental feeding practices are evaluated through a self-reported questionnaire, Food Parenting Practices Questionnaire, with three subscales (Child's Intake Self-regulation Practices, Food Availability and Accessibility Practices, and Ineffective Control Practices) developed and adapted to the Portuguese population within this study. Parents answer to 40 items on a 5-point Likert scale (from Totally false to Totally true). Higher values on each subscale indicate a more frequent use of this type of parental feeding practices. The total mean score of each subscale ranged from 1 to 5.", 'timeFrame': 'Baseline, immediately after the intervention, 3 months after the intervention, 6 months after the intervention'}

Please estimate the sample size based on the assumption: 
An alpha level of 0.05, power of 0.80, a moderate correlation pattern between time measurements of 0.35, and a dropout rate of 50% were assumed.
Power and sample size
        Statistical power analysis was performed for sample size estimation based on published data regarding this topic using G*Power 3.1.9.2. For our repeated measures within-between group comparison study, we used Cohenâs f criteria and considered a small effect size of 0.15 [8, 31], an alpha equal to 0.05, and power of 0.80 for a two-group with four repeated measures design (with a moderate correlation pattern between time measurements of 0.35). The sample size needed is approximately 130 participants (i.e., 65 parents in each of the two-arm groups), but the total sample size was adjusted to account for a dropout rate of 50% [32, 33]. Therefore, the sample will be collected until 130 participants in each group (N = 260) enroll in the study. Our proposed sample size will also be adequate for multilevel modeling with level 1 repeated measures nested within level 2 individuals, by assuring a minimum of 50 individuals required for level 2 [34].