In my opinion it depend on what the objective(s) of your study. If you want to asses the effectiveness of mebendazole to treat certain disease/condition that affect not only the children but also their family members and the close contacts, the second criteria is more suitable. But, if you want to asses the effect of mebendazole to treat the disease just among 3 to 7 year old children (just want to know the effectiveness on children), the first criteria you should consider.

In my point of view that if you are going to assess the effectiveness of mebendazole among 3 to 7 year old children, in the inclusion criteria you should add 3-7 years old children.

The aim of the inclusion/exclusion criteria is to reduce the number of variables that may influence the effect size of your intervention. Your participant is the child, as it is for them that you are assessing effectiveness (not the family, if I understand your question correctly). You are trying to create a 'pure' perfect population of participants where the only effect difference between your control group and your test group will be due to the intervention. Therefore, if you know that a factor will effect the result of the intervention, you can try to standardise that across your population with you inclusion/exclusion criteria. Thus you might make your inclusion criteria:

- child age 3-5 years

- confirmed diagnosis of .... according to ........

- no co-morbidities

- family members willing/able to concurrently take medication.

Or perhaps more appropriately you might specify the concomitant family treatment as part of your study protocol. As the carer needs to provide informed consent for participation in the research trial, the family will need to agree to also take the medication if they are participating in the trial. You could also add an extra arm to the study that compares the effect of your medication with and without family treatment.

Whichever way, if you suspect that family treatment will alter the medication effect on your subject (the child), then you need to monitor family adherence to their meds as well as the child's in case there is an influence on the actual effect of the medication. Potentially, variable adherence by family members could dilute the actual effect so that your study does not show an effect even if there is a true effect there.

you can refer to Iranian web site www.irct.ir and take help finding from some investigates for determine appropriate exclusion/inclusion criteria for your own study designing on future.

The inclusion/exclusion criteria will depend on the objective of your study, the target population (specific patients, age groups, ethnicity...) and of course the intervention itself.

As mebendazole therapy is recommended to all the family members to break the cycle of re-infection that is frequent roundworms, then this should be included as part of the treatment protocol although they won't be as part of the target population to be evaluated. But by unifying this prerequisite among all participants, you will avoid any possible bias.

Accordingly, the inclusion criteria would be children aged between 3 to 7 years only, and in the methods section you will elaborate among the concomitant family treatment as part of the treatment protocol. In anyways, you will be getting the consent form from the adult family members who will be informed about the study protocol and the therapeutic intervention.

I totally agree with Susan, if I'm understanding well the aim of your study. Family members are a covariate and need to be reported in the inclusion criteria. If you want to evaluate the effect of your drug on childrens when also parents are under the same drug treatment, if you do not add both on the inclusion criteria you cannot control and objectivate your specific requirement (combined treatment of children and parents). On the same way, to no add parents in the inclusion criteria, can create confusion among your coworkers.