Problem when acessing a list from another script? (ArgumentOutOfRangeException)

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Edit: With the tip given by @gjf, i have changed in the parent script the function "Start" to "Awake", in this way i guarantee that the list is created before the child objects try to load, preventing the error posted below.

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Ok guys, my situation is this:

I have an single empty GameObject that hold another three empty GameObjects (childs).

When i'm acessing a list inside the parent object trough the script inside the childs, or give a debug.log for example, it returns this error:

"ArgumentOutOfRangeException: Argument is out of range. Parameter name: index"

The parent has this script attached to him:

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 public class Master : MonoBehaviour {


 public List<int> randOrder;
 
 void Start() {
     
     randOrder = new List<int>();
     
     for(int i=0;i<3;i++){
         randOrder.Add(Random.Range(1,4));
     }
     
 }
 }

The other three child objects has this script attached to then:

 public class childObject : MonoBehaviour {
 
 public Master masterRef; // hold the reference to the Master script.

  void Start(){ 
             
     masterRef = gameObject.GetComponentInParent<Master>(); //Reference of the Master script.

     Debug.Log(masterRef.randOrder[0]); // The error happens here
     Debug.Log(masterRef.randOrder[1]); // And here
     Debug.Log(masterRef.randOrder[2]); // And here

  }
 }

What could be the problem? The list seems to be empty when accessed by another script, although it is not.

The complete error is this:

 ArgumentOutOfRangeException: Argument is out of range.
 Parameter name: index
  System.Collections.Generic.List`1[System.Int32].get_Item (Int32 index) (at /Users/builduser/buildslave/mono-runtime-and-classlibs/build/mcs/class/corlib/System.Collections.Generic/List.cs:633)