旋转带有附属子对象的GameObject (Unity 2D)

所以我得到这个代码来实例化我的游戏对象大炮，它有一个孩子"球"附加到它。当我使用左/右方向键时，我试图将"球"旋转到"大炮"周围。

using UnityEngine;
using System.Collections;
public class NewBehaviourScript : MonoBehaviour {
    public GameObject Cannon = null;
    public float speed = 1.0f;
    void Start () {
         Cannon = Instantiate (Resources.Load ("Prefabs/Cannon")) as GameObject;
    }
    // Update is called once per frame
    void Update () {
        if (Input.GetKey(KeyCode.LeftArrow)){
            Cannon.transform.Rotate(Vector3.left * speed * Time.deltaTime);
        }
        if (Input.GetKey(KeyCode.RightArrow)){
            Cannon.transform.Rotate(Vector3.right * speed * Time.deltaTime);
        }
    }
}