Well this is my Enemy Script:

 public class Enemy : MonoBehaviour
{
    public GameObject explosion;
    public float speed;
    public float shotDelay;
    public GameObject enemyBomb;
    public bool canShot;
    public int pointValue = 30;


    IEnumerator Start()
    {
        GetComponent<Rigidbody2D>().velocity = Vector2.right * speed;
        if (canShot == false) yield break;

        while (true)
        {
            for (int i = 0; i < transform.childCount; i++)
            {
                Instantiate(enemyBomb, transform.position, transform.rotation);
            }
            yield return new WaitForSeconds(shotDelay);
        }
    }

    private void OnTriggerEnter2D(Collider2D collision)
    {

        FindObjectOfType<Score>().AddPoint(pointValue);
        Instantiate(explosion, transform.position, transform.rotation);
        Destroy(gameObject);

    }
    private void OnBecameInvisible()
    {
        Destroy(gameObject);
    }
}

The problem is, that the enemy shoots before he is visible so there is no chance to fight him. Is there a way how to check if the Enemy is visible or not?