Would you say they should or shouldn't be allowed to?

Not sure your relation to "Johnny"'s case, but in reality, modern medicine has a better reputation, so if taken into a foster home, they will be expected to use the most widely accepted form of medical care. In some situations, what is known as "alternative" or "holistic" medication has been used on kids with health problems and the parents have been charged with neglect. The social worker has both the responsibility and the duty to do this. The foster parents can do whatever they want technically too.