In PHP, I must require_once() the classes of the objects I want to put in session before session_start().
If I want to put in session an instance of a class which is a child of a parent class, can I just require_once() the parent class, or do I need to list all the children classes?
If I understand you correctly (assuming that you have individual files with each class), you will need to
require_oncethe file/class for the parent and the child class (otherwise the child class won’t know it’s parent class).session_startshould really have nothing to do with it.