This is an interesting question. Let me give you what I think is the best scenario.
First, there are so many different ways of communication today that we should rule out some of them as impersonal. So, I would say that you should not communicate these important matters either over the phone or via email. In short, it should be done in person.
Second, I would say that the context is also important. The best place is probably at the school or daycare center itself. In this way, you can show the parents what the day will be like. You can also show the facilities and the staff or teachers who work in the place. You would also be able to show other details, such as the food and rest area (if it is a daycare). As they say a picture is worth a thousand words.