I have parents give me a list of who (other than them) is allowed to pick up the children. The parents also usually tell me ahead of time or call to say that someone else is picking up. I have also had parents tell me if they need to come by to drop off a sweater, extra training pants, etc. I make sure that the child is distracted and far away from the door so that they don't see mommy or daddy coming in and we avoid the meltdown.