Instantiating child as parent not working : Object Pooling

I am making an endless runner game, and I am trying to use Object Pooling. When I try to set the transform of the child to the transform of the parent, it gives me an error:

  NullReferenceException: Object reference not set to an instance of an object(wrapper stelemref) object:stelemref (object,intptr,object) ObjectPool.Start () (at Assets/Scripts/LevelScripts/     ObjectPool.cs:19)

Here is the code. Any answers are good! Thank You!

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ObjectPool : MonoBehaviour {
 
     private GameObject[][] objects = null;
 
     public GameObject[] objectsToInstantiate1;
     public GameObject[] objectsToInstantiate2;
     public GameObject[] objectsToInstantiate3;
     public GameObject[] objectsToInstantiate4;
     public GameObject[] objectsToInstantiate5;
 
     // Use this for initialization
     void Start () {
         objects = new GameObject[5][];
         for (int i = 0; i < objectsToInstantiate1.Length; i++) {
             objects [1] [i] = Instantiate (objectsToInstantiate1[i]) as GameObject;
             objects [1] [i].transform.parent = gameObject.transform;
             objects [1] [i].SetActive (false);
         }
         for (int j = 0; j < objectsToInstantiate2.Length; j++) {
             objects [2] [j] = Instantiate (objectsToInstantiate2[j]) as GameObject;
             objects [2] [j].transform.parent = gameObject.transform;
             objects [2] [j].SetActive (false);
         }
         for (int k = 0; k < objectsToInstantiate3.Length; k++) {
             objects [3] [k] = Instantiate (objectsToInstantiate3[k]) as GameObject;
             objects [3] [k].transform.parent = gameObject.transform;
             objects [3] [k].SetActive (false);
         }
         for (int l = 0; l < objectsToInstantiate4.Length; l++) {
             objects [4] [l] = Instantiate (objectsToInstantiate4[l]) as GameObject;
             objects [4] [l].transform.parent = gameObject.transform;
             objects [4] [l].SetActive (false);
         }
         for (int m = 0; m < objectsToInstantiate5.Length; m++) {
             objects [5] [m] = Instantiate (objectsToInstantiate5[m]) as GameObject;
             objects [5] [m].transform.parent = gameObject.transform;
             objects [5] [m].SetActive (false);
         }
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 }