collision with instantiated prefabs child

Im instantiating a prefab and that prefab has childs. The childs tagged like “enemy” and when i instantiating a bullet to the childs they are not destroyed. It’s working with parent prefabs but not working with childs of that prefabs. How can i solve this problem??
my code:

private GameObject enemy;
// Start is called before the first frame update
void Start()
{
    enemy = GameObject.FindGameObjectWithTag("enemy");
    
}

private void OnCollisionEnter(Collision collision)
{
    if (collision.gameObject.tag == "enemy")
    {
        Debug.Log("touched");
        Destroy(enemy);
    }
    
}

The attached children from the parent have an enemy tag? Add a tag into them and also a collider to detect the collision.