Instantiating Cube Prefabs with scale

First You need to Define what the localsize of the Objects is:

Here is a simple Version, you have to Setup your Prefab correctly:
Make an Empty GameObject, then Add as Example a Cube to it. Make it a Prefab and Implement it in the Unity Inspector to the brickParent object.

Parent Objects should always be on Scale 1, so we gonna scale the localSize of the Child Object, scaling the Parent Objects can often causes huge problems later in development Stages.

     public class UnityAnswer : MonoBehaviour
     {
     //Setup the Prefab correct, Empty Gameobject LocalScale 1 and the Cube (other Object) as Child Object of the Empty GameObject
         public GameObject brickParent;
     
         public int gridWidth = 10;
         public int gridDepth = 10;
         public int gridHeight = 10;
     //Define the Size of your Objects
         public float localScale = .5f;
     
         // Start is called before the first frame update
         void Start()
         {
             for (int y = 0; y < gridHeight; y++)
             {
                 for (int z = 0; z < gridDepth; z++)
                 {
                     for (int x = 0; x < gridWidth; x++)
                     {
 //We Instantiate the GameObject and the Position of x/y/z * localScale so we can Access it
                         GameObject go = Instantiate(brickParent, new Vector3(x * localScale, y * localScale, z * localScale), Quaternion.identity) as GameObject;
 //Since we only have One Child (The Cube as Example) we get the First Child (Dont mess around with GetComponentInChildren because GetComponentInChildren doesnt really works like its Named it always will start with GetComponent and get the Parent Object
                         Transform t = go.transform.GetChild(0);
 //We Scale the Child Object to the new localScale
                         t.localScale = new Vector3(localScale, localScale, localScale);
                     }
                 }
             }
         }    
     }

Here is the same Approach just with 2 additional Methods to show you how you chould Change the Grid then in Runtime

 using System;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Random = UnityEngine.Random;
 
 public class UnityAnswer : MonoBehaviour
 {
 
     public GameObject brickParent;
 
     public int gridWidth = 10;
     public int gridDepth = 10;
     public int gridHeight = 10;
 
     public float localScale = .5f;
 
     List<GameObject> gridObjects = new List<GameObject>();
 
     // Start is called before the first frame update
     void Start()
     {
         for (int y = 0; y < gridHeight; y++)
         {
             for (int z = 0; z < gridDepth; z++)
             {
                 for (int x = 0; x < gridWidth; x++)
                 {
                     GameObject go = Instantiate(brickParent, new Vector3(x * localScale, y * localScale, z * localScale), Quaternion.identity) as GameObject;
                     Transform t = go.transform.GetChild(0);
                     t.localScale = new Vector3(localScale, localScale, localScale);
                     gridObjects.Add(go);
                 }
             }
         }
     }
 
     private void Update()
     {
         if (Input.GetKeyDown(KeyCode.Alpha1))
         {
             RefreshLocalScale();
         }
 
         if (Input.GetKeyDown(KeyCode.Alpha2))
         {
             NewGrid();
         }
     }
 
     private void RefreshLocalScale()
     {
         localScale = Random.Range(.5f,2f);
         if (gridObjects.Count > 0)
         {
             foreach (var item in gridObjects)
             {
                 item.transform.position = new Vector3(item.transform.position.x * localScale, item.transform.position.y * localScale, item.transform.position.y * localScale);
                 Transform t = item.transform.GetChild(0);
                 t.localScale = new Vector3(localScale, localScale, localScale);
             }
         }
     }
 
     private void NewGrid()
     {
         localScale = 1.5f;
 
         if (gridObjects.Count > 0)
         {
             foreach (var item in gridObjects)
             {
                 Destroy(item);
             }
         }
         gridObjects.Clear();
 
         for (int y = 0; y < gridHeight; y++)
         {
             for (int z = 0; z < gridDepth; z++)
             {
                 for (int x = 0; x < gridWidth; x++)
                 {
                     GameObject go = Instantiate(brickParent, new Vector3(x * localScale, y * localScale, z * localScale), Quaternion.identity) as GameObject;
                     Transform t = go.transform.GetChild(0);
                     t.localScale = new Vector3(localScale, localScale, localScale);
                     gridObjects.Add(go);
                 }
             }
         }
     }
 }