I would just call her/email her and say, it was so nice to meet her and her son however, something has come up and you will no longer be able to fill the spot...you will spread the word for them to other providers in the area. and thats that. I would NEVER take an older child unless all kids in care were older, too much dif dynamic to caring for that big of an age dif. older kids drive me bonkers, repectful or not.