Reasonable Time-frame to hear back from parents?

[Momof4]

Does anyone ever followup within the week (if you haven't heard back right away) and say you'd like to offer them the spot if you really liked the family? Or does that seem too desperate?

I always send a thank you & nice to meet you email with my contracts and other forms attached for them to look over after an interview because I don't want to waste all my paper and ink. I ask them to feel free to write back to me with any further questions they may have but hopefully they will either let me know if they are 'going in another direction' or if they are very interested in a space. Since I always let them know during the interview that I have several interviews set up and the decision will be made in a certain amount of time if they are really interested they get back to me quickly. If you never hear from them again and they weren't even courteous enough to send you an email then you didn't want them anyway!