parenting instantiated object

if i have a prefab such as a ball and i want to instantiate it and then parent it under a another object how do i do this to the instantiated game object and not its prefab? example:

var ball : GameObject;

Instantiate(ball,transform.position,transform.rotation)
ball. transform.parent = transform

it does not work because ball is a prefab. how do i do it to the instantiated object and not the prefab it was instantiated from?

Simply assign a variable to hold the instance identity. instead of calling instantiate on its own, you can do:

var myObject : GameObject = Instantiate(ball,transform.position,transform.rotation);
myObject.transform.parent = transform;

consider you are going to make "board " as parent and "ball" as a child means....

var myObject : GameObject = Instantiate(ball,transform.position,transform.rotation);
myObject.transform.parent = GameObject.Find("board").transform;