I moved within the same town and every single family followed me to the new home. When we moved we found the new house first, then sold our home. I think that it helped because the families knew exactly where i was moving to so that they could make an informed decision. Moving out of town is a different story. I think that i would give my families as much notice as possible. Knowing that usually you have a 60 days closing will give the parents time to find other care. I would most likely want to use past parents as refrences in my new town so i'd like to stay on their "good side".