How to find a specific clone of a prefab and access its children

I have a prefab which has 3 child text objects. How to access it in clones? GameController script:

 using UnityEngine;
 using System.Collections;
 
 public class GameController : MonoBehaviour {
 
     public GameObject drop;
     public Vector3 spawnValues;
 
     public float spawnWait;
     public float startWait;
     public float waveWait;
 
 
     // Use this for initialization
     void Start () {
         StartCoroutine(Rain());
     }
     
     IEnumerator Rain()
     {
         yield return new WaitForSeconds(startWait);
         while(true){
             for (int i = 0; i < 5; i++){
                 Vector3 spawnPosition = new Vector3(Random.Range(-spawnValues.x, spawnValues.x),
                                spawnValues.y, spawnValues.z);
                 Instantiate (drop, spawnPosition, Quaternion.identity);
                 yield return new WaitForSeconds(spawnWait);
             }
             yield return new WaitForSeconds(waveWait);
         }
     }
 }

And script attached to prefab:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class DropFaller : MonoBehaviour {
 
     float speed;
     Vector3 movement;
 
     int number_1;
     int number_2;
     string sign;
 
     TextMesh nOneText;
     TextMesh nTwoText;
     TextMesh signText;
 
     void Start(){
         nOneText = GameObject.FindWithTag("number_1").GetComponent<TextMesh>();
         nTwoText = GameObject.FindWithTag("number_2").GetComponent<TextMesh>();
         signText = GameObject.FindWithTag("sign").GetComponent<TextMesh>();
 
         number_1 = Random.Range(1, 100);
         number_2 = Random.Range(1, 100);
         sign = "+";
         nOneText.text = number_1.ToString();
         nTwoText.text = number_2.ToString();
         signText.text = sign;
 
         speed = Random.Range(-0.06f, -0.01f);
         movement = new Vector3(0f, speed, 0f);
     }
     
     void FixedUpdate () {
         gameObject.transform.position += movement;
     }

}

But this code on each instantiation changes text for same object instead of setting to new clones. I tried to change GameObject to gameObject, or use GameObject.gameObject - nothing works. Is there way to access specific instance, something like self or this or whatever? Or should I use arrays or a hashtables?