The most developmentally appropriate way in this situation would be: Routinely have the student say goodbye to his family and start an activity
For small kindergarten children, the crying is most likely caused by the fear of being separated from the family and not being taken back.
In order to handle this, the best way is to make sure that the child accept the fact that his/her family only leave him/her for a while before coming back. This could be achieved by making that child say goodbye before class activities.