The people on this list are only expected to be in the nursery in the event that a guest (visitor) would want to their child to attend the nursery so that they could attend the liturgy.  Once the usher knows that the guest is in need of nursery services the usher will let the person whose name is on that date know that they are needed in the nursery.  The parish members who wish for their children/grandchildren to spend time in the nursery are expected to stay in the nursery with their children/grandchildren.