Creating mouse controlled car camera (New to unity)

Hello, i am new to unity and i am trying to create a camera that rotates around the car along the Y and X axis.
I have put the MainCamera as a child of my car, so it follows the car arround.

Rotating the camera around its own axis works, but i dont know what to do to make the camera rotate around the car.

This is how i rotate the camera around its own axis:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class OrbitCamera3 : MonoBehaviour {
5.  
6.     public float sensitivityX = 5f;
7.     public float sensitivityY = 5f;
8.  
9.     public float minimumX = -100f;
10.     public float maximumX = 100f;
11.  
12.     public float minimumY = -45f;
13.     public float maximumY = 45f;
14.  
15.     float rotationY = 0f;
16.     float rotationX = 0f;
17.  
18.     // Update is called once per frame
19.     void Update ()
20.     {
21.             rotationY += Input.GetAxis ("Mouse Y") * sensitivityY;
22.             rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
23.  
24.             rotationX += Input.GetAxis ("Mouse X") * sensitivityX;
25.             rotationX = Mathf.Clamp (rotationX, minimumX, maximumX);
26.  
27.             transform.localEulerAngles = new Vector3 (-rotationY, rotationX, 0);
28.     }
29. }

But when i try to rotate the camera around the car, the camera just keeps spinning. I guess i am using the wrong input for "RotateAround" but i cant find any alternatives.
This is my attempt:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class OrbitCamera3 : MonoBehaviour {
5.  
6.     public GameObject player;
7.     public Transform center;
8.  
9.     public float sensitivityX = 5f;
10.     public float sensitivityY = 5f;
11.  
12.     public float minimumX = -100f;
13.     public float maximumX = 100f;
14.  
15.     public float minimumY = -45f;
16.     public float maximumY = 45f;
17.  
18.     float rotationY = 0f;
19.     float rotationX = 0f;
20.  
21.     // Use this for initialization
22.     void Start () {
23.         player = GameObject.FindWithTag ("Player");
24.             center = player.transform;
25.     }
26.     // Update is called once per frame
27.     void Update ()
28.     {
29.             rotationY += Input.GetAxis ("Mouse Y") * sensitivityY;
30.             rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
31.  
32.             rotationX += Input.GetAxis ("Mouse X") * sensitivityX;
33.             rotationX = Mathf.Clamp (rotationX, minimumX, maximumX);
34.  
35.         transform.RotateAround (center.position, Vector3.up, rotationX);
36.         transform.RotateAround (center.position, Vector3.left, rotationY);
37.         transform.LookAt (center);
38.  
39.  
40.     }
41. }

Thanks for any help that might put my in the right direction