public class GameManager : MonoBehaviour {

    BackgroundGenerator backgroundGenerator;

    void Start () {
        backgroundGenerator = GetComponent<BackgroundGenerator>();
        backgroundGenerator.GenerateBackground(new Vector2(transform.position.x, transform.position.y), new Quaternion(0, 0, 0, 0));
    }

    void Update () {

    }
}

public class BackgroundGenerator : MonoBehaviour {

    public GameObject sky01;
    public GameObject mountains01;

    public float forest01Speed = 50;
    public float mountains01Speed = 1;

    Forest forest;

    void Start () {
        forest = GetComponent<Forest>();

    }

    void Update () {

    }

    public void GenerateBackground(Vector3 position, Quaternion rotation)
    {
        Instantiate(forest01, position, rotation);
        Instantiate(mountains01, position, rotation);
        Instantiate(sky01, position, rotation);
    }
}