How to reactivate a gameObject?

Just take it back one step...

Make an empty GameObject and put the object you want to enable/disable grouped as a child.

Take the script you were using on the now child object and put it on the parent.

You can declare a GameObject var in this script, and attach the child to it in the Inspector. Then, enable/disable this child object, instead of just using gameObject.active = false.

This way, your invisible parent object is always active to control the state of the actual object you want to toggle.

I did it that way and it works but my child does't move anymore.

Here's a code that disable my additional enemy on start and reactivate it when player has 200 points.

 using UnityEngine;
 using System.Collections;
 
 public class EnemyActivatorController2 : MonoBehaviour {
 
     // Use this for initialization
     void Start () {
         GameObject ActiveEnemy2 = GameObject.Find ("EnemyActivator2");
         foreach (Transform child in ActiveEnemy2.transform) {
                         child.gameObject.SetActive (false);
                 }
 
 
     }
     
     // Update is called once per frame
     void Update () {
         if (PlayerController.Points == 200) {
             GameObject ActiveEnemy2 = GameObject.Find ("EnemyActivator2");
             foreach (Transform child in ActiveEnemy2.transform) {
                 child.gameObject.SetActive (true);
             } 
         }
     
     }
 }

It working but my additional enemy spawn and doesn't move anymore.

Here is enemy script:

 using UnityEngine;
 using System.Collections;
 
 public class EnemyController2 : MonoBehaviour {
 
     public float speed = -1;
     private Transform spawnPoint;
 
     // Use this for initialization
     void Start () {
         spawnPoint = GameObject.Find("SpawnPoint").transform;
         rigidbody2D.velocity = new Vector2 (speed, 0);
 
 
 
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     void OnBecameInvisible()
     {
         if (Camera.main == null)
                         return;
 
         float yMax = Camera.main.orthographicSize - 0.5f;
         transform.position = new Vector3( spawnPoint.position.x,
                                          Random.Range (-yMax, yMax),
                                          transform.position.z );
     }
 
 }
 
 

Any ide how to make he move again?