Shooting at the nearest enemy automatically.

Hi guys. I want to create a script which will automatically shoot at the nearest enemy. I have an enemies empty object which I spawn all of my enemies to (Every enemy is the child of enemies). It should work like a turret. I've already write it but it doesn't work correctly and I don't know why. It only shoot to a fix point. What do you think the problem is?

 using UnityEngine;
 using System.Collections;
 
 public class AllyAI : MonoBehaviour {
 
     public GameObject enemiesParent;
     public float Damage = 100;
     public GameObject Effect;
     public float fireRate = 10;
 
     private Transform nearestEnemy;
     private float nearestEnemyDistance;
 
     void Start()
     {
         nearestEnemyDistance = Mathf.Infinity;
     }
 
     void Update () {
         if (enemiesParent.transform.childCount > 0)
         {
             Shoot(NearestEnemy(enemiesParent));
         }
     }
 
     Transform NearestEnemy (GameObject Parent)
     {
         foreach (Transform child in Parent.transform)
         {
             float currentDistance = Vector3.Distance(this.transform.position, child.position);
             if (currentDistance < nearestEnemyDistance)
                 nearestEnemy = child;
         }
         return nearestEnemy;
     }
 
     void Shoot(Transform Target)
     {
         RaycastHit hit;
         Ray ray = Camera.main.ScreenPointToRay(Target.position);
 
         if (Physics.Raycast(ray, out hit))
         {
             GameObject effectClone = (GameObject)Instantiate(Effect, hit.point, Quaternion.LookRotation(hit.normal));
             if (hit.transform.CompareTag("enemy"))
             {
                 hit.transform.SendMessage("ApplyDamage", Damage, SendMessageOptions.RequireReceiver);
             }
             Destroy(effectClone.gameObject, 1);
         }
 
     }
 
     IEnumerator Wait(float time)
     {
         yield return new WaitForSeconds(time);
         Debug.Log("Wait");
     }
     
 }