Problem with GetComponentinChildren and Instantiate

Hello, I'm trying to make a code that allow me with little mesh called modules to procedurally create a dungeon. My modules have empty gameObject has children named exit. My goal is to make 2 exits of 2 different modules match in the world space. To do that, i was thinking that i could recuperate the transform.position of my exit with the command GetComponentInChildren. Also i'm "spawning" my module in the world with a Instantiate command but if i try to get the transform.position of my exit, it gives me the position of the prefab (0,0,0) and not the child but the parent transform.

 using UnityEngine;
 using System.Collections.Generic;
 
 public class WorldGenerator : MonoBehaviour {
 
     public GameObject Modules;
     public GameObject StartModule;
 
     public int itt = 5;
     private Vector3 Exit;
     private Vector3 ModExit;
     // Use this for initialization
     void Start () {
         ////////It's where i'm blocking
         GameObject startmodule = (GameObject)Instantiate (StartModule, transform.position, transform.rotation);
         Exit = startmodule.GetComponentInChildren<Transform>().position;
 //////////////////////////////////////////////////////////////
         Instantiate (Modules, Exit, transform.rotation);
         ModExit = Modules.GetComponentInChildren<Transform> ().position;
 
         Debug.Log (Exit); //return (0,0,0), the prefab transform in my prefab folder
         Debug.Log (ModExit);
 
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 }
 

I tried to store my Instantiate into a variable and then ask the transform to this variable but it still give me 0,0,0. Help will be appreciated and thanks for your response.

PS : My script is attached to an empty gameobject in my scene PS2 : sorry for killing Shakespeare language