You could have an agreement called a “right of first refusal.” This is a common provision which reads that if one parent who has the kids is gone for more than 4 hours, s/he will call the other parent and offer them the “right” to parent the kids before anyone else. If the other parent is busy, then Parent #1 can leave the kids with a responsible person of their choice. In the past this has created a great deal of litigation and is not a favored provision by most judges.