Accessing object within list

Question

I have a parent object Z which contains a list of child objects.  I would like to access the properties of the child objects within the list.

 

I wrote code to access the first object in the list.  The code compiles correctly but returns a (object reference not set to instance of an object) error when I run the application.

 

Here is part of the code:

 

zparentobject= new Zclass();

childclass zchildobject = new childclass();

zchildobject=zparentobject.listz[0];  * source of error*

 

Help?