OnDrag with Instantiated gameObject

I have tested it in Unity with a sample project. It works fine.

1) The parent is the object on which we tap. There is no need of them to be in a parent child hierarchy.

2) The child is the objects which gets instantiated and starts taking touches.

3) Have tested it on UI object with canvas screen space as camera

4) Both the parent and the child have EventSystems the IDragHandler. When the parent spawns the child , the OnDrag method of the parent passes the PointerEventData to the child. This will make the screen touched go in the sequence: parent -> child. Here the parent is taking the touches but it is passing it on to the child and hence the child moves

I would recommend you to create a sample project, get a hold of how it is working and then apply it to your project.

The parent script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.EventSystems;
 
 public class parent : MonoBehaviour , IPointerDownHandler , IPointerUpHandler , IDragHandler , IBeginDragHandler , IEndDragHandler
 {
     public GameObject childPrefab , instantiatedChild;
 
     //script of the child to get the drag method
     private child childScript;
 
     void Start()
     {
         //cache the prefab
         childPrefab = Resources.Load("child") as GameObject;
     }
 
     public void OnPointerDown(PointerEventData data)
     {
         print("mouse down");
         StartCoroutine("Instantiator");
     }
 
     public void OnBeginDrag(PointerEventData data)
     {
         if (instantiatedChild != null)
         {
             childScript = instantiatedChild.GetComponent<child>();
         }
     }
     public void OnDrag(PointerEventData data)
     {
         if (instantiatedChild != null)
         {
             childScript.OnDrag(data);
         }
     }
     public void OnEndDrag(PointerEventData data)
     {
         instantiatedChild = null;
         childScript = null;
     }
     
     public void OnPointerUp(PointerEventData data)
     {
         //if mouse Up is before 2 seconds, it will not instantiate
         StopCoroutine("Instantiator");
     }
 
     IEnumerator Instantiator()
     {
         yield return new WaitForSeconds(2);
         GameObject go = Instantiate(childPrefab, transform.parent, false ) as GameObject;
         instantiatedChild = go;
     }
 }
 

The child/object which will get the drag after instantiation:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.EventSystems;
 
 public class child : MonoBehaviour , IDragHandler
 {
 
     private Transform thisTransRef;
 
     void Start()
     {
         thisTransRef = transform;
     }
 
     public void OnDrag(PointerEventData eventData)
     {
         var world_point_mousePos = Camera.main.ScreenToWorldPoint(new Vector3(eventData.position.x, eventData.position.y,Mathf.Abs( Camera.main.transform.position.z)));
 
         thisTransRef.position = world_point_mousePos;
     }
 
 }