NullReferenceException and script load order

My problem is that I need to have a class with a variable that holds the count of a number of entities with another class.

To try and solve the problem I have put together some code that simplifies the process:

ChildClassA.cs

using UnityEngine;
using System.Collections;

public class ChildClassA : MonoBehaviour
{

		void OnEnable()
		{
		ControllerClass.childA.entityCount++;
		}

		void OnDisable()
		{
		ControllerClass.childA.entityCount--;
	        }
}

ChildClassAData.cs

using UnityEngine;
using System.Collections;

public class ChildClassAData : MonoBehaviour
{
	public int entityCount = 0;

}

ControllerClass.cs

using UnityEngine;
using System.Collections;

public class ControllerClass : MonoBehaviour
{

	public static ChildClassAData childA;
	    
		// Use this for initialization
		void Awake ()
		{
		    childA = GetComponent<ChildClassAData> ();    		     
		}
	
		// Update is called once per frame
		void Update ()
		{
		    Debug.Log ("A: " + childA.entityCount);    		
		}


}

I receive no Compiler Errors.

When running the game I get a NullReferenceException which I assume is because the child class has tried to access the childA object before it is initialized. If any more of the object are created after this error the code runs smoothly.

Therfore I would like to know how to have the instances of the child class wait for the controller class to be fully initialized before being enabled.

As this is only a problem for the child’s that are there at the start I found a work around as below:

ChildClassA.cs

using UnityEngine;
using System.Collections;

public class ChildClassA : MonoBehaviour
{
	public static bool initialized = false;
	
		// Use this for initialization
        void Start ()
	{

	     if (!initialized) {  
		ControllerClass.childA.entityCount++;
		initialized = true;
			}
	}
	
		
	void OnEnable()
	{

		if (ControllerClass.childA != null && initialized) {
			ControllerClass.childA.entityCount++;
		}
	}


	void OnDisable()
	{
		ControllerClass.childA.entityCount--;
	}

}