unity get child gameobject

//Instantiate Prefab
GameObject originalGameObject  = Instantiate(prefab);

//To find `child1` which is the first index(0)
GameObject child2 = originalGameObject.transform.GetChild(0).gameObject;

//To find `child2` which is the second index(1)
GameObject child2 = originalGameObject.transform.GetChild(1).gameObject;

//To find `child3` which is the third index(2)
GameObject child3 = originalGameObject.transform.GetChild(2).gameObject;

GameObject originalGameObject = GameObject.Find("MainObj");
GameObject child = originalGameObject.transform.GetChild(0).gameObject;